Guide 01
CRP in IBD
What CRP measures, why it can rise in inflammation, and why some people can flare with a normal result.
Open guideFrom a Biomedical Scientist in the NHS
I’ve spent over a decade working as a Biomedical Scientist within the NHS, analysing blood and stool samples every day. I’ve seen how results like CRP, calprotectin and haemoglobin are used to guide decisions — but also how often patients are left without clear explanations.
This hub is designed to bridge that gap. To take what happens behind the lab doors and translate it into something practical, honest and easy to understand.
Start here
Core lab guides for IBD
Each one of these guides is created around the most common tests we use in IBD to monitor disease progression and therapy response. Each guide is written within the context of inflammatory bowel disease, whether that be UC, Crohn's or microscopic colitis.
Guide 02
Faecal calprotectin
What the number means, why it matters, and when a high result usually leads to further review.
Open guide
Guide 03
Full blood count
A simple breakdown of haemoglobin, white cells and platelets, with the context IBD patients actually care about.
Open guide
Guide 04
B12/Folate/Iron Deficiency
Why is B12/Fol and iron deficiency is so common in IBD and how we can spot the early trends before symptoms present
Open guide
Guide 05
Biopsies
What happens to the biopsies once collected for your colonoscopy?
Open guide
Guide 06
ESR
The decade old test for inflammation still used today. Estimated Sedimentation Rate is an important test in conjunction with others, but should never solely be relied on.
Open guide Lab guide
CRP (C-Reactive Protein) in IBD
An overview of CRP testing and how it is used to monitor inflammation in Crohn’s disease and ulcerative colitis.
What is this test?
When inflammation kicks off in the body, this is one of the first, most reliable biomarkers. While not specific to IBD (not used to diagnose) it’s valuable to measure treatment response and flare progression. Released as part of the first line (innate) immune response - ill spare you details of much of its function. Partly because it’s complicated, partly because it’s just boring (sorry biochem colleagues)!
We spin your sample down, this separates the blood cells, platelets and clotting factors from the bit we want for this test - the serum. The serum, a yellow liquid contains all the proteins, including CRP. We then use a ‘high-sensitivity immunotrimeric assay’. Which essentially means we add a reagent that binds to the CRP protein, then we shine a light through it. Depending on how much this light scatters will give us a CRP result. Clever huh!
Best practices for sample collection (sample type)
A blood sample for this test is usually taken by a nurse or phlebotomist, so there is very little you need to do yourself. However, there are a few important things worth being aware of.
Always make sure your sample is correctly labelled at the time of collection:
You’d be surprised how often we receive samples with the wrong patient details, and unfortunately these have to be rejected for safety reasons. In the lab, we rely entirely on that label matching you.
Order of sample collection:
You may also notice multiple tubes being taken. The order in which these are filled (known as the order of draw) is important, as certain additives in tubes (like anticoagulants) can contaminate other samples if taken in the wrong sequence. In routine bloods, this is the correct order: coagulation sample (often green or blue lids), serum (often yellow or gold lids) and EDTA (often purple or red lids).
Most routine tests only require a small volume of blood:
It is important we receive enough blood to do the test. In the lab though for CRP we only need around 0.5ml (min). We will always try our best, but don't panic, if you think the nurse is sending a very small sample if you are difficult to bleed.
Why has my doctor ordered it?
Detects active inflammation: CRP rises quickly (within 6–8 hours) when inflammation flares — whether in the gut or elsewhere. It’s often used alongside faecal calprotectin to confirm whether a flare is truly inflammatory or more functional (like IBS).
Tracks disease activity:
Falling CRP levels after treatment suggest inflammation is settling. Persistently high levels can indicate ongoing disease activity or infection.
Helps distinguish flare vs. infection:
While both can raise CRP, very high levels (e.g. >100 mg/L) tend to point toward infection or severe inflammation.
Monitors treatment response:
Gastro teams use CRP trends to check whether biologics, steroids, or immunosuppressants are doing their job.
What it can and cannot tell you
CRP can indicate that inflammation is present in the body, but it cannot tell you where that inflammation is coming from.
In IBD, it is often used as a general marker of disease activity, but it is not perfect. Some patients — particularly those with ulcerative colitis — may not produce a strong CRP response even during an active flare.
This is thought to be partly due to individual biological and genetic differences in how the liver produces CRP in response to inflammation. As a result, a normal CRP does not always mean the disease is under control, which is why it is usually interpreted alongside other markers such as faecal calprotectin and clinical symptoms.
📊 Typical Reference Ranges
Note: each lab may establish its own ranges and cut-offs based on its local population. These are a rough guide only.
Normal: 0 – 5 mg/L
Mild elevation: 5 – 30 mg/L → low-grade inflammation or mild flare
Moderate: 30 – 100 mg/L → active inflammation
High: > 100 mg/L → severe inflammation or infection
>300 mg/L and we are likely calling the on-call doctor to potentially wake you up and bring you into AE.
Questions to ask your doctor
The most important question for your doctor (as with most tests) is: are there any trends in my CRP?
How has CRP changed in conjunction with my ESR? (ESR changes are slower than CRP, so may still be raised while CRP is returning to normal — suggesting inflammation is settling)
Does my CRP usually rise during a flare, or am I someone who doesn’t produce a strong CRP response?
How does my CRP compare with my symptoms? (Do they match, or is there a disconnect?)
Should we be checking faecal calprotectin alongside CRP to get a clearer picture of gut inflammation?
What level of CRP would concern you in my case, and at what point would it trigger further investigation or treatment changes?
Lab guide
Faecal Calprotectin
A stool test commonly used to detect intestinal inflammation.
What is this test?
Oh Faecal Calprotectin, how many colonoscopies you have potentially avoided. You have my thanks. Let’s talk about this test, first identified in the early 1990’s, but only widely adopted in the NHS years later. (I could write an entire post on NHS bureaucracy… unless you prove a test saves a load of money, it doesn’t get adopted.) Fast forward to 2015–2018, and this test finally became routine. It’s now an essential tool for monitoring disease, treatment response, and helping diagnose IBD. (Not perfect for everyone, more on that later.) It’s often difficult to distinguish between IBS and IBD. That leads to unnecessary colonoscopies (hello money-saving!). Calprotectin allows doctors to tell the two apart quickly and safely. If you were diagnosed before this test existed (like me in 2013), it often meant being poked, prodded, and having the C-word thrown in. Faecal calprotectin would have smoothed that journey massively. That’s why it’s one of my favourite tests and a genuine success story for the NHS and for IBD care.
Indications for Testing
- Marker for acute inflammation,
- Estimation of gastrointestinal inflammation degree,
- Parameter for monitoring Crohn’s disease, ulcerative colitis or the patient’s status after removal of polyps,
- Discrimination between patients with inflammatory bowel disease (acute Crohn’s disease and ulcerative colitis) and irritable bowel syndrome without the need for colonoscopy.
What is Faecal Calprotectin?
Calprotectin is a calcium/zinc-binding protein complex released by neutrophils (the most abundant type of white blood cell) acting as part of the innate/first responder immune response. Neutrophils release calprotectin anywhere in the body where inflammation occurs, but only gut inflammation causes it to appear in stool, which is why this test works.
Neutrophils (the big pink ones, red cells behind them) - always like the ones that look like smiley faces.
Best practices for sample collection
💩 My tips for collecting a stool sample (faecal calprotectin):
You only need a tiny amount.
Around a pea-sized portion (50–100 mg) is enough. Patients often send far more than the lab needs — but it’s the quality, not the quantity, that matters.
Use the right container.
Always use the calprotectin kit or pot provided by your GP or hospital. Many have built-in spoons or collection sticks in the lid.
You would be surprised by some of the containers people send samples in.
True story: I once received a full stool inside a Morrisons shopping bag… please don’t do that!
True story: I once received a full stool inside a Morrisons shopping bag… please don’t do that!
Take the sample from a representative area.
If the stool looks normal, take it from the middle rather than the surface — this gives a more accurate result.
If the stool is loose or mixed with mucus, collect a small portion that reflects the overall sample.
Avoid visible blood or large amounts of mucus where possible, as these can artificially elevate results or create variability.
Keep it clean.
Avoid contamination with urine, toilet water, or cleaning products. Many people find it easier to use plastic wrap or a clean disposable container placed in the toilet to catch the sample.
Label it clearly and return it promptly.
Samples must include correct identifiers (forename, surname, date of birth, and NHS or hospital number). Even small errors can lead to rejection.
Faecal calprotectin is relatively stable, but best practice is to return the sample within 24–48 hours. If needed, store it in the fridge (not the freezer) until drop-off.
Timing doesn’t need to be exact.
There is no need to fast or collect at a specific time. Try to provide a sample that reflects your usual symptoms rather than an unusually good or bad day.
What Does Calprotectin Do? Why Do Neutrophils Release It?
1) It’s an antimicrobial weapon.
Calprotectin binds the metal ions zinc and manganese, which bacteria and fungi need to grow.
Rather than directly attacking them, it starves them. A strategy known as “nutritional immunity.”
2) It amplifies and regulates inflammation
This is part of why IBD becomes a problem. The double edged sword of any auto-immune condition.
Calprotectin acts as a distress signal called DAMP (Damage-Associated Molecular Pattern). It binds to immune receptors like TLR4 and RAGE, triggering cells to release inflammatory messengers called cytokines (IL-1β, IL-6, TNF-α). These cytokines are a focus of much research in regards to IBD.
In infection this keeps you alive. In IBD, the system misfires and becomes chronic.
3)It helps neutrophils survive in hostile environments
Inflamed tissues are acidic, hot (think fevers), and filled with reactive chemicals. Calprotectin helps neutrophils stabilise themselves so they can keep fighting.
Summary: Calprotectin isn’t “just something we measure”, it’s a powerful tool the immune system uses. We just take advantage of the fact it calprotectin in the stool is a measurable protein directly proportional to the inflammation in the gut.
How we test it in the lab?
Send me some poo.
We don’t need much (actually 15mg, which is pea sized).
Don’t get it contaminated with toilet water! (My preferred method is to put lots of toilet roll in the bowl first to catch it).
Blood and mucus is ok in sample, dont aim for it, don’t avoid it. The idea here is to get a good representative sample of the overall stool. Like a mini poo :)
The sample is stable for 3 days at room temperature, but we prefer to receive it the same day. We store it at 2–8°C and test it within 48 hours.
If frozen at –20°C, it’s stable for 12 months. Though freezing can sometimes cause a slight artificial increase, because neutrophils may burst and release more calprotectin. Your lab/doctor will likely take this into consideration when interpreting results so it isn’t an issue.
The ELISA Method (How the Test Actually Works)
1. Your sample, along with standards and controls (these are known results we use to make sure the result is correct), is added to a test plate. The plate is already coated with special antibodies that specifically capture calprotectin.
2. If calprotectin is present, it sticks to the plate.This happens during the first incubation step.
3. A second antibody is added that attaches to the captured calprotectin.This second antibody has an enzyme attached to it. So now you have a “sandwich”: Antibody — Calprotectin — Enzyme-linked Antibody.
4. A colour-forming solution is added.The enzyme reacts with this solution (called TMB), turning it blue, and then yellow when the reaction is stopped.
5. The strength of the yellow colour reflects how much calprotectin is in your sample.A stronger colour = more calprotectin, a weaker colour = less calprotectin
6. A calibration curve is used to calculate your exact result.The machine compares your sample to known standards and produces a real number (e.g., 75 µg/g, 500 µg/g, etc.)
This is why it’s such a reliable, quantitative test for inflammation.
Result Interpretation and Reference Ranges
First my disclaimer! Results can give strong evidence, but a doctor is always best for advice as they will look at the whole clinical picture. My job is to give a number based only on the sample i receive, their job is to diagnose!
Each lab may establish their own reference ranges based on their local population. As confusing as that sounds, there may be small differences. Also, these reference ranges are based on the test kit: Manual — IDK® Calprotectin (MRP8/14). Widely used within the NHS UK.
Reference Ranges for Faecal Calprotectin in ADULTS (>12 years old):
Konikoff MR & Denson LA (2006) Inflamm Bowel Dis 12:524–534 doi:10.1097/00054725-200606000-00013
Important: Make sure you check the units your lab is reporting in, and convert if required!
| Category | Value | Interpretation |
|---|---|---|
| Median (healthy adults) | 25 µg/g | Typical baseline |
| < 50 µg/g | Negative | No significant inflammation |
| 50–100 µg/g | Borderline positive | Repeat test recommended |
| > 100 µg/g | Positive | Suggests inflammation |
Note: Many confounding factors can cause increased levels of faecal calprotectin in the absence of IBD or IBD in a quiescent disease phase, e.g. use of NSAIDs (non-steroidal anti-inflammatory drugs), any intercurrent gastrointestinal infection, and the presence of malignancies. These factors should be considered in the interpretation of the test results and therapy of IBD.
Normal Ranges for Faecal Calprotectin in Paediatrics (0 - 12 years Old)
Hestvik E et al. (2011) BMC Pediatrics 11:9 doi:10.1186/1471-2431-11-9
Method: 302 apparently healthy children, age 0–12 years, in Kampala, Uganda, were tested for faecal calprotectin concentration.
Table 1: Faecal calprotectin concentration in apparently healthy children by age.
95% confidence interval (95% CI) is indicated in brackets.
| Age | Number (%) | Median calprotectin [µg/g] (95% CI) |
|---|---|---|
| 0–3 months | 14 (4.6%) | 345 (195–621) |
| 3–6 months | 13 (4.3%) | 278 (85–988) |
| 6–12 months | 27 (8.9%) | 183 (109–418) |
| 1–4 years | 89 (29.5%) | 75 (53–119) |
| 4–12 years | 159 (52.6%) | 28 (25–35) |
Normal Ranges for Faecal Calprotectin in Paediatrics (4 - 17 years Old)
Fagerberg UL et al. (2003) J Pediatr Gastroenterol Nutr 37:468–472
Method: 117 healthy children age 4–17 years were tested for faecal calprotectin concentration.
Table 2: Faecal calprotectin concentration in healthy children by age.
| Age | Number | Median faecal calprotectin [µg/g] |
|---|---|---|
| 4–6 years | 27 | 28.2 |
| 7–10 years | 30 | 13.5 |
| 11–14 years | 27 | 9.9 |
| 15–17 years | 33 | 14.6 |
Conclusion: The suggested cut-off level for adults (< 50 µg/g) can be used for children aged 4–17 years.
FAQ's
FAQ’s
Faecal calprotectin FAQ’s
Common questions about faecal calprotectin, stool testing, interpretation and when colonoscopy is still needed.
1. Is there a test better than a Faecal Calprotectin?
Yes there is: The excretion of Indium-111-labelled neutrophilic granulocytes has been suggested as the “gold standard” of disease activity in inflammatory bowel disease. However, measuring 111-indium-labelled granulocytes is very costly (patient’s hospitalisation, analysis and disposal of isotopic material) and is connected with radioactive exposition of the patients. For this reason, a repeated application to children and pregnant women is not recommended.
For the NHS - this isn’t available - and frankly, wouldn’t be needed in 99% of cases in my opinion.
2. Does a high faecal calprotectin always mean IBD?
No.
Calprotectin rises whenever neutrophils enter the gut – and that can happen for several reasons:
- Gastroenteritis (viral or bacterial)
- Food poisoning
- NSAIDs (ibuprofen, naproxen)
- Coeliac disease
- Diverticulitis
- Post-polypectomy
- GI bleeding
- After intense exercise
A single elevated result does not equal IBD. Doctors look at the full clinical picture, this will include symptoms, trends and repeat tests.
3. Can IBS raise faecal calprotectin?
No.
IBS does not cause inflammation, so calprotectin stays normal.
4. How quickly does calprotectin respond to treatment?
Usually 2–8 weeks, depending on:
- Steroids → fast drop
- Biologics → slower but steady
- Mesalazine → moderate drop
- Antibiotics → varies
Regular tests help us so much. It’s hard to make conclusions on one sample alone, but repeating (as annoying as it is) is so important. Trends are crucial for good interpretation.
5. What are the best practices for stool collection?
Pea sized amount. Good representation of the overall stool (think mini poo). Don’t aim for blood and mucus, but don’t avoid it either. Same day collection is best at room temp, but freezing may be required logistically. Don’t contaminate itwith water!
6. Is faecal calprotectin raised in cancer? Is colonoscopy the only way to know?
I’m always careful discussing cancer because it’s easy for fear to take over, so please trust your doctor’s interpretation here.
When interpreting patients results, this is where medical experience really plays. It’s hard to explain how we develop this almost sixth sense. When you interpret these results all day long, subtle differences in the overall picture (I can't stress this enough, the whole story of the patient is considered) can be glaringly obvious to the professional that a colonoscopy must be performed urgently. We will highlight it with a phone call, the doctor will also recognise it.
There is overlap in colorectal cancers and IBD symptoms. There’s no hard or fast rules I can put into a clear table. Plus, if IBD isn’t in remission all that cell repair puts you more at risk of developing cancer. Hence, the 5 year colonoscopies (don't miss your next one!)
If we look at faecal calprotectin alone, it is simply a marker of inflammation, not cancer itself. Calprotectin can be elevated in colorectal cancer or polyps, but that’s because these conditions provoke local inflammation, not because calprotectin is a cancer signal. It rises because neutrophils release calprotectin in response to irritation in the gut, and that irritation can come from many causes.
In fact, levels in cancer are often much lower than what we see in active IBD, and cancer is far less common than infections, IBS/IBD overlap, or benign inflammatory conditions.
So while cancer can raise calprotectin, a high result does not mean cancer - it simply tells us that inflammation is present and needs investigating.
Doctors will interpret the full clinical picture based on:
- Symptoms (e.g., persistent change in bowel habit, weight loss, blood mixed in stool, low haemoglobin/anaemia, usually in people over 40–50)
- Lots of blood testsand the relationship between them can give clues
- And if there is any concern, a colonoscopywith histological interpretation is the definitive test. This is also the reason regular colonoscopies once diagnosed with IBD is VERY important.
Bottom line:Calprotectin alone can’t indicate if it's cancer or IBD. However, in combination with other tests and symptoms it may highlight the urgency of performing a colonoscopy (which will give you all the answers).
If there is one thing I would advise, is, you know your body. All the tests in the world won’t beat a colonoscopy. If you want, it's your right to demand a colonoscopy - that will give you a definitive answer.
7. Why do I need a colonoscopy if I can just test faecal calprotectin?
In short, you can’t beat a colonoscopy. It's the ‘gold standard test’. Faecal Cal has its place in differentiating between IBS and IBD, monitoring IBD disease progression and response to treatment. However, as healthcare professionals it's our job to rule things out. A colonoscopy will give you a much more definitive answer than any non-invasive, in-vitro sample.
8. Does a negative Calprotectin = no inflammation?
Lot’s of people have asked me this: I have all the symptoms of a flare, but my results appear normal. Why?
I really tried hard to find an answer for this (it's quite common!). It’s possible to get a false negative for example, say you diluted it with toilet water, maybe that particular stool sample wasn’t collected correctly, lab errors, very early flare activity. But if it’s been repeated and your bloods (I.E. CRP) are all negative as well, these are my thoughts and reasoning why:
1. Proctitis (rectal only): probably the biggest reason may be that inflammation is right at the end of the bowel, the stool may pass above the inflamed area before calprotectin has a chance to mix through it.
Mine started as proctitis (it's since spread up a little bit). My CRP and FC (faecal calprotectin where always low, but a colonoscopy diagnosed it. When it spread up a little bit, suddenly FC was high, my CRP was relatively
2. IBS overlay: a colonoscopy would show active inflammation and prove me wrong. However it may be that the symptoms are overlapping whilst in IBD remission. IBS won’t have blood, but other than that, the symptoms can be fairly similar!
3. CRP non-responders: This is certainly a known thing, and not anything to worry about. 20 - 30% of patients can be non-responders. Causes can be genetic, and seem to be more common in UC than Crohn's.
Lewis JD (2011) Gastroenterology 140:1817–1826 doi:10.1053/j.gastro.2010.11.058
D’Haens G et al. (2012) Inflamm Bowel Dis 18:2218–2224 doi:10.1002/ibd.22917
So unfortunately, that was the best I could find or think of - it just happens to some patients. To be honest, if your results are normal, it isn’t saying you don’t have IBD or invalidating your symptoms. It's saying your body is doing a fairly good job handling it. That’s a good thing!
9. Do you get used to testing poo?
Yup! I only added this bit to get one point across. Don't ever be embarrassed.
Aside from our duty to remain professional, you really do get de-sensitised to it. Its just poo. I mean, obviously im going to wear gloves/PPE and use a fume cupboard. But if you think i haven't seen worse than yours, i have. It doesn't bother us, and it shouldn't bother you.
Questions to ask your doctor
If there’s one theme here, it’s this: trends and context matter more than a single number.
Here are some useful questions you can ask to get more value from your results:
-
Are there any trends in my calprotectin results over time?
One result is just a snapshot — patterns over time are far more meaningful. -
How does this result compare with my previous tests?
Even a “normal” result might be important if it’s changed significantly for you. -
Does this result match my symptoms?
Sometimes the numbers and how you feel don’t align — that’s important to explore. -
Could anything else be causing this result?
Infection, medication (like NSAIDs), or recent illness can all affect calprotectin. -
Should this test be repeated?
Borderline or unexpected results are often best interpreted with a repeat sample. -
Do I need further investigation, like a colonoscopy?
Calprotectin is a guide — not a diagnosis. Sometimes a direct look is still needed. -
How does this relate to my other blood tests (CRP, ESR, FBC)?
Looking at everything together gives a much clearer picture than one test alone. -
What does this mean for my treatment plan?
Is treatment working? Do we need to adjust anything? -
What level would concern you enough to act?
Understanding your doctor’s thresholds helps you interpret future results.
Final thought: Your symptoms matter just as much as your results. If something doesn’t feel right, push for answers — you know your body better than anyone.
Lab guide
Full Blood Count (FBC)
A routine blood test that measures red cells, white cells and platelets.
What is this test?
This one’s my baby since I specialised in hematology.
We use an analyser called the Sysmex XN (best in the biz) - each capable of running 100 samples an hour, and we have 6 of them all on a giant scalextric (for all the 90s kids) style track.
When your doctor requests a full blood count, it's broken down into 13 parameters, looking at red cells, white cells and platelets. Each parameter and the relationship between the values can teach us a lot about what’s happening in your body, from inflammation to iron/B12/folate deficiency.
Best practices for sample collection (sample type)
For a Full Blood Count, we require a standard blood sample taken into a purple, or red (EDTA) tube.
The good news: this part has very little to do with you — a nurse or phlebotomist will take the sample.
We only need a small amount of blood for the test, but sample quality is absolutely critical. If the sample isn’t collected or handled properly, it can affect the accuracy of the results. The sample for best results should be tested within <8 hours from sample collection. If this isn't possible its recommended to refrigerate at 2 - 8 degrees.
Occasionally, we may see unusual or unexpected results and ask for a repeat sample — not because something is wrong with you, but because the sample itself may not be reliable.
One of the most common issues we see is clotted samples. This can happen if the blood isn’t mixed properly in the tube when taken, or if the collection was a bit difficult (for example, if you’re a tricky bleed and the sample is taken slowly or with some resistance). Unfortunately, if a sample is clotted, we can’t analyse it — and it will need to be repeated.
There’s also something called the order of draw. When multiple blood tubes are taken, the order matters to prevent cross-contamination between additives in the tubes. This is something your healthcare professional is trained in, but it’s a good example of how small details can impact results.
One thing you can help with: always check that your details on the sample tube are correct. You’d be surprised how often samples arrive labelled for the wrong patient. Your sample should include your name, date of birth, and NHS or hospital number — if in doubt, double check before you leave.
What we learn from an FBC in IBD
Anaemia (low red blood cells or haemoglobin):
Common in IBD due to chronic inflammation, blood loss, or nutrient malabsorption (like iron, B12, or folate).
- Low Hb, low MCV → iron deficiency.
- Low Hb, high MCV → B12/folate deficiency.
Inflammation:
Ongoing inflammation often drives up white blood cells (WBCs), especially neutrophils. A raised platelet count (thrombocytosis) is also a classic sign of active inflammation in IBD.
Infection:
Flares and infections can look similar symptomatically. However looking at the individual white cells (remember white cells can be broken into 5 types: Neutrophils, lymphocytes, monocytes, eosinophils, basophils) we can differentiate between infection and inflammation, or even allergic responses such as parasitic infections.
Medication monitoring:
Some IBD drugs (like azathioprine or mercaptopurine) can suppress bone marrow. Regular FBCs help ensure your white cell and platelet counts stay within safe ranges.
Recovery or remission:
When inflammation settles, white cells and platelets often fall back to normal, and red cells gradually recover — so trends over time can tell a reassuring story.
What it can and cannot tell you
It shows blood cell levels but does not identify the underlying cause of abnormal results.
Reference ranges (guide only)
Important disclaimer:
I work in the NHS in the UK, but every laboratory may establish its own reference ranges based on its local population, analyser platform, and internal validation data. These ranges are a guide only and should never override the range printed on your own result. Your doctor or clinical team should always interpret the result in the context of your symptoms, trend over time, medication, and the rest of your bloods.
I work in the NHS in the UK, but every laboratory may establish its own reference ranges based on its local population, analyser platform, and internal validation data. These ranges are a guide only and should never override the range printed on your own result. Your doctor or clinical team should always interpret the result in the context of your symptoms, trend over time, medication, and the rest of your bloods.
Basic adult FBC guide ranges (UK / NHS style):
A quick nod to Barbara Bain — the queen of haematology in my eyes. If you work in haematology in the UK, chances are you’ve learned something from her.
On mobile, swipe sideways to view the full table.
| Parameter | Typical adult range | Units | What it can suggest if low / high |
|---|---|---|---|
| Haemoglobin (Hb) – men | 130–180 | g/L | Low: anaemia. High: dehydration, smoking, hypoxia, less commonly polycythaemia. |
| Haemoglobin (Hb) – women | 115–165 | g/L | Low: anaemia. High: dehydration, smoking, hypoxia, less commonly polycythaemia. |
| Red cell count (RBC) – men | 4.5–6.5 | x10¹²/L | Low: anaemia / marrow suppression. High: dehydration or increased red cell production. |
| Red cell count (RBC) – women | 3.8–5.8 | x10¹²/L | Low: anaemia / marrow suppression. High: dehydration or increased red cell production. |
| Haematocrit (Hct) – men | 0.40–0.54 | L/L | Low: anaemia. High: dehydration or true red cell increase. |
| Haematocrit (Hct) – women | 0.37–0.47 | L/L | Low: anaemia. High: dehydration or true red cell increase. |
| Mean cell volume (MCV) | 80–100 | fL | Low: iron deficiency / thalassaemia trait. High: B12 or folate deficiency, alcohol, liver disease, some drugs. |
| Mean cell haemoglobin (MCH) | 27–32 | pg | Low: often parallels iron deficiency / microcytosis. High: often tracks with macrocytosis. |
| Mean cell haemoglobin concentration (MCHC) | 320–370 | g/L | Usually less dramatic clinically; can help support red cell interpretation. |
| Red cell distribution width (RDW) | 11.5–15.7 | % | High: more variation in red cell size, often seen in iron deficiency, mixed deficiencies, or recovery states. |
| White cell count (WBC) | 3.6–11.0 | x10⁹/L | Low: viral illness, marrow suppression, drugs. High: infection, inflammation, steroids, stress response. |
| Neutrophils | 1.8–7.5 | x10⁹/L | High: bacterial infection, inflammation, steroids. Low: some viral illness, drugs, marrow suppression. |
| Lymphocytes | 1.0–4.0 | x10⁹/L | High: viral patterns, some chronic immune or haematological causes. Low: steroids, acute illness, immunosuppression. In children, lymphocyte counts are often physiologically higher than in adults. |
| Monocytes | 0.2–0.8 | x10⁹/L | High: chronic inflammation, recovery from infection, some haematological causes. |
| Eosinophils | 0.1–0.4 | x10⁹/L | High: allergy, asthma, eczema, parasites, some drug reactions. |
| Basophils | 0.02–0.10 | x10⁹/L | Usually a small player; persistent elevation can occasionally matter in specialist haematology contexts. |
| Platelets | 140–400 | x10⁹/L | High: inflammation, iron deficiency, recovery states. Low: infection, immune causes, drugs, marrow issues, clumping artefact. |
Practical interpretation tips for patients:
- Don’t interpret a single number in isolation. The trend matters more than one snapshot.
- Hb + MCV + MCH together often give the first clues to iron deficiency or B12 / folate deficiency.
- White cells and platelets can rise with active inflammation in IBD, but also with infection or steroid treatment.
- A “normal” result doesn’t always mean “nothing is going on”. Results must be interpreted alongside symptoms and the rest of your bloods.
- Children are different. In particular, lymphocyte counts are often higher in children than in adults, so paediatric ranges should be used.
- Your lab’s own range wins. If your printed reference range differs slightly from this table, use the one on your result.
Reference note: This table is intended as a simple patient guide for UK readers and reflects common NHS-style adult haematology ranges rather than a single universal standard.
Questions to ask your doctor
With a Full Blood Count, it’s all about patterns and relationships between results — not just one number.
Here are some useful questions to help you get more from your results:
-
Are there any trends in my results over time?
One result is just a snapshot — changes over time tell a much clearer story. -
Do my haemoglobin, MCV and MCH suggest iron deficiency or B12/folate deficiency?
These values together often give the biggest clues about the type of anaemia. -
Are my white cells and platelets raised due to inflammation or something else?
In IBD, these can rise with inflammation — but infection, stress and medication can also affect them. -
Do my results match my symptoms?
Sometimes the numbers and how you feel don’t align — that’s important to explore. -
Could my medication be affecting these results?
Some IBD treatments can suppress bone marrow and affect white cells or platelets. -
Is there any evidence of infection?
Looking at the breakdown of white cells can sometimes help differentiate infection from inflammation. -
Do I need further tests based on this result?
For example: iron studies, B12/folate, CRP, or further investigations. -
What result would concern you enough to act?
Understanding your doctor’s thresholds helps you interpret future results with confidence.
Final thought: A Full Blood Count is one of the most powerful screening tools we have — but only when interpreted in context. If something doesn’t feel right, trust your instincts and ask the question.
Lab guide
B12/Folate and Iron Deficiencies
B12/Folate and Iron deficiencies are all too common in IBD. Quite often they can be missed for a long time until you're out of breath and symptomatic anaemia has kicked in. Here's everything you need to know, and how to spot them to act sooner.
What is B12/Folate and Iron?
They are essential vitamins needed to make new cells. Especially red blood cells (the part of your blood that carries oxygen to your cells). Tired walking up the stairs? Memory loss, heart palpitations? They impact your quality of life massively, and are easily treatable.
Essential means the body can’t naturally produce them - so you must acquire them from your diet.
B12 (aka Cobalamin): Needed for DNA synthesis, red blood cell production, and nerve function; Found mainly from animal products (meat, eggs, dairy); Absorbed in the terminal ileum (in Crohn’s this is a common inflammatory hot spot).
Folate (aka Vitamin B9): Also essential for DNA synthesis; Found in green vegetables, legumes, fortified foods; Folate stores are small (weeks–months) and therefore more common in the general population; Absorbed in the small intestine.
Iron: Required to make haemoglobin, the molecule that carries oxygen; Found in red meat, legumes, leafy greens; Absorbed in the duodenum and jejunum.
Small intestine diagram showing where B12, folate and iron are absorbed.
Why is B12 and Folate linked together?
The short answer is: having plenty of Folate is pointless without plenty of B12, and vice versa. They are biochemically intertwined through something called the methyl-folate trap. One becomes trapped (and therefore functionally deficient) if the other is missing. This is why we always check them together.
How do we identify deficiencies in the lab?
The Full Blood Count (FBC)
Let's first focus on spotting B12/Folate and Iron deficiencies in an FBC. Why? Because it’s one of the most routine tests your doctor will order. Every time blood is taken, an FBC is almost always run. This is why spotting early warning signs within these results can be crucial.
Blood samples being loaded and processed for Full Blood Count testing on the analyser.
How to Spot B12/Folate Deficiencies in an FBC (Megaloblastic Anaemia)
Increased Mean Corpuscular Volume (MCV): MCV looks at the size of the red cell. When DNA synthesis is impaired due to a deficiency in B12/Fol, red cells do not divide efficiently. This means they grow into large red cells known as Macrocytes and Megaloblasts. These are hallmark features of B12/Fol deficiency. The result is fewer red cells overall, meaning less oxygen delivered to your body — leaving you tired or short of breath.
Typically this would show as an MCV >108 fL and should trigger B12/Fol levels to be tested.
Comparison of normal red blood cells and macrocytic cells seen in B12/Folate deficiency.
Low Haemoglobin: Haemoglobin is the molecule within a red cell that carries oxygen. This measures the total oxygen-carrying capacity of your blood. When red cell production is impaired, fewer cells are released → less haemoglobin overall.
Normal haemoglobin ranges:
Men: ~130–180 g/L
Women: ~115–165 g/L
Mild anaemia: Men: ~110–129 g/L. Women: ~100–114 g/L.
Severe anaemia: <80 g/L
Increased Mean Corpuscular Haemoglobin (MCH): Each enlarged red cell carries more haemoglobin than normal, so MCH increases.
Hypersegmented Neutrophils on the blood film: Abnormal FBC results will prompt a blood film review. A classic feature of B12/Folate deficiency is hypersegmented neutrophils — another key clue for further testing.
Hypersegmented neutrophils seen on blood film — a classic feature of B12/Folate deficiency.
SPOT TRENDS: If your MCV is rising while your haemoglobin is falling, this should prompt B12/Folate testing before symptoms develop.
How to Spot Iron Deficiency (Microcytic Anaemia) in an FBC
Low Haemoglobin: Haemoglobin is an iron-based molecule. Without enough iron, the body cannot produce adequate haemoglobin.
The body will compensate for reduced oxygen over time, but trends over months can reveal iron deficiency before symptoms appear. Symptoms range from mild fatigue to severe anaemia and pallor.
Normal haemoglobin ranges:
Men: ~130–180 g/L
Women: ~115–165 g/L
Mild anaemia: Men: ~110–129 g/L. Women: ~100–114 g/L.
Severe anaemia: <80 g/L
Reduced Mean Corpuscular Volume (MCV): Red cells become smaller (microcytic) as the body produces lower-quality cells in an attempt to maintain oxygen delivery.
Microcytic red blood cells seen in iron deficiency — smaller and less effective at carrying oxygen.
Reduced Mean Corpuscular Haemoglobin Concentration (MCHC): Without iron, red cells contain less haemoglobin (hypochromic), reducing oxygen delivery to tissues.
Blood Film: Confirms findings — small, pale red cells with variation in size and shape.
Blood film showing variation in red cell size and shape in iron deficiency.
Microscope used in the lab to review blood films and confirm abnormalities.
SPOT TRENDS: If haemoglobin, MCV, MCH and MCHC are all trending downwards, this suggests depleting iron stores — act before symptoms occur.
I've spent a good chunk of time on the FBC because, while doctors may not always request Iron/B12/Fol levels directly, they almost always request a Full Blood Count. Watching trends in haemoglobin, MCV, MCH and MCHC can highlight problems early — often before symptoms even begin.
Summary flow chart showing how trends in FBC parameters can help identify B12, folate and iron deficiencies.
How to test directly for B12/Folate and Iron/Ferritin levels
While the FBC gives strong clues, these deficiencies are confirmed using direct biochemical tests. These are run on large automated analysers in the lab, capable of processing thousands of samples daily.
Our biochemistry analysers (affectionately known as Velma) process tests including B12, Folate, Iron, Ferritin, CRP, liver function and more.
Reference ranges (B12/Folate deficiency)
Reference ranges can vary between laboratories depending on the analyser used and the local population. These values should be used as a general guide only and always interpreted alongside clinical context and trends over time.
| Test | Typical Reference Range | What to look for |
|---|---|---|
| Vitamin B12 | ~180–900 ng/L | Low levels suggest deficiency |
| Folate | ~3–20 µg/L | Low levels suggest deficiency |
| MCV | ~80–100 fL | >108 fL may indicate B12/Folate deficiency |
| MCH | ~27–33 pg | Often increased in macrocytic anaemia |
| Haemoglobin | Men: ~130–180 g/L Women: ~115–165 g/L | Low levels indicate anaemia |
SPOT TRENDS: Rising MCV with falling haemoglobin should prompt B12/Folate testing — even before symptoms appear.
Reference ranges (Iron deficiency)
Reference ranges can vary between laboratories depending on the analyser used and the local population. These values should be used as a general guide only and always interpreted alongside clinical context and trends over time.
| Test | Typical Reference Range | What to look for |
|---|---|---|
| Ferritin | ~30–300 µg/L | Low ferritin is a strong indicator of iron deficiency |
| MCV | ~80–100 fL | <75 fL suggests microcytic anaemia |
| MCH | ~27–33 pg | <27 pg suggests reduced haemoglobin per cell |
| MCHC | ~300–360 g/L | <300 g/L suggests hypochromic cells |
| Haemoglobin | Men: ~130–180 g/L Women: ~115–165 g/L | Low levels indicate anaemia |
SPOT TRENDS: Falling haemoglobin alongside decreasing MCV, MCH and MCHC suggests depleting iron stores — act early before symptoms develop.
Questions to ask your doctor
If you're experiencing symptoms or have abnormal results, here are some useful questions to help guide the conversation:
- Could my fatigue or shortness of breath be related to low haemoglobin, B12, folate or iron levels?
- Are my results trending in the wrong direction, even if they are still within the normal range?
- Would it be appropriate to check my B12, folate and ferritin levels based on my FBC results?
- Could inflammation be affecting my ferritin result?
- Are there any signs of early anaemia in my blood results?
- Do my red blood cell indices (MCV, MCH, MCHC) suggest a developing deficiency?
- Could my diet, medications, or underlying condition (e.g. IBD) be contributing to these levels?
- Should these tests be repeated in a few months to monitor trends?
- At what point would treatment or supplementation be recommended?
- Are there any additional tests needed to confirm the cause of these results?
REMEMBER: You don’t need to have severe symptoms to ask these questions. Trends in your blood results can often highlight problems early — before they start affecting your day-to-day life.
Lab guide
Colonoscopy and Biopsies
What happens to your biopsies after a colonoscopy — and what doctors are actually looking for under the microscope.
What happens to my biopsies after a colonoscopy?
During a colonoscopy, small pieces of tissue called biopsies may be taken from the bowel lining. These are placed into a histology pot, usually containing formalin preservative, and sent to the histology laboratory.
A histology pot used to collect biopsy samples before they are sent to the histology laboratory.
Histology is a specialised department within the medical laboratory. Their job is to study the microscopic anatomy of biological tissues. They are a highly specialised team with an important responsibility.
The tissue is preserved, embedded in wax, sliced into extremely thin sections, stained, and then examined under the microscope.
Biopsy tissue is embedded in wax, cut into extremely thin slices, stained, and then visualised under the microscope.
The tissue sections are incredibly thin — typically around 3–5 micrometres thick (around 0.003 mm), thinner than a human hair.
IMPORTANT: Some conditions — particularly microscopic colitis — may appear completely normal during colonoscopy and can only be diagnosed under microscopic examination.
What are doctors looking for under the microscope?
To the untrained eye, histology slides can look like random pink and purple patterns. To an experienced histopathologist though, they know exactly what normal bowel tissue should look like — and more importantly, what abnormal tissue looks like.
Normal colon under H&E stain. The crypt architecture and intestinal wall can be assessed under the microscope.
In inflammatory bowel disease (IBD), doctors are looking for patterns of inflammation and damage within the bowel lining.
Depending on the condition, this may include:
- Increased inflammatory cells within the mucosa
- Crypt distortion or crypt abscesses
- Ulceration or erosion of the bowel lining
- Granulomas (sometimes seen in Crohn’s disease)
- Architectural changes suggesting chronic inflammation
- Thickened collagen bands (microscopic colitis)
- Increased lymphocytes within the bowel lining
- Pre-cancerous cellular changes (dysplasia)
Special stains can also be used to highlight certain structures or immune cells more clearly.
REMEMBER: Histology is often considered the gold standard for diagnosing many bowel conditions because it allows doctors to assess disease at a cellular level.
Why can colonoscopies sometimes look normal?
Not all bowel inflammation is visible to the naked eye.
In conditions like microscopic colitis, the bowel may appear completely normal during colonoscopy. The inflammation is only visible once tissue samples are examined under a microscope.
This is why biopsies are extremely important — even if the bowel “looks fine” during the procedure.
It also explains why some patients experience severe symptoms despite apparently normal colonoscopy findings or blood tests.
KEY POINT: A “normal looking” colonoscopy does not always rule out inflammation or disease.
How long do biopsy results usually take?
Histology takes longer than routine blood tests because the tissue has to go through several preparation stages before it can be examined.
Typically the process includes:
- Fixation in formalin preservative
- Embedding in paraffin wax
- Cutting ultra-thin tissue sections
- Applying stains
- Microscopic examination by a pathologist
Depending on workload, complexity, and whether additional stains are needed, results may take anywhere from several days to a few weeks.
What histology can and cannot tell you
Histology is extremely powerful, but it still needs to be interpreted alongside symptoms, scans, blood tests, stool tests, and colonoscopy findings.
Biopsies can help:
- Confirm inflammation
- Distinguish Crohn’s disease from ulcerative colitis
- Diagnose microscopic colitis
- Identify infection or abnormal cells
- Detect dysplasia or cancerous change
However, biopsies cannot always predict symptom severity, future flare-ups, or exactly how someone will respond to treatment.
Questions to ask your doctor
- Did my biopsies show active inflammation?
- Were there any signs of chronic damage or architectural change?
- Did the histology suggest Crohn’s disease, ulcerative colitis, or microscopic colitis?
- Were any additional stains or specialist tests required?
- Was there any dysplasia or pre-cancerous change?
- If the colonoscopy looked normal, did the biopsies still show abnormalities?
- Do my biopsy findings match my symptoms and blood results?
- Will I need repeat colonoscopies or surveillance biopsies in future?
REMEMBER: Histology results are one piece of the puzzle. Doctors combine them with symptoms, scans, bloods, stool tests and colonoscopy findings to build the full picture.
Lab guide
ESR (Erythrocyte Sedimentation Rate)
One of the oldest inflammation tests still widely used in modern medicine. Simple in concept, but often misunderstood in IBD.
What is this test?
Full disclaimer. ESR is probably my least favourite inflammation marker in IBD.
However, you have to respect a laboratory test that has survived for over 100 years.
ESR stands for Erythrocyte Sedimentation Rate. It measures how quickly red blood cells settle to the bottom of a tall tube over time.
When inflammation is present, proteins in the blood, particularly fibrinogen, cause red blood cells to stick together and form stacks called rouleaux.
These heavier stacks fall faster through the plasma, resulting in a higher ESR result.
The concept is actually incredibly simple. You literally watch how quickly the red cells fall over an hour.
The more inflammatory proteins present, the heavier the red cell clumps become, meaning they sediment faster.
The red cells settle at the bottom of the tube, leaving clearer plasma above.
ESR methodology. Red blood cells gradually settle to the bottom of the tube. Faster settling can indicate higher levels of inflammation.
The problem is that ESR is extremely non-specific. Many different things can affect how quickly red cells settle.
This is why ESR should never be interpreted alone.
Dr. Alf Westergren. Pioneer of the Westergren ESR method still widely used in laboratories over 100 years later.
It is easy to take laboratory medicine for granted today, but pioneers like Westergren helped lay the foundations for how we diagnose and monitor inflammatory disease.
LAB PERSPECTIVE: ESR remains heavily requested despite its limitations. In IBD, CRP and faecal calprotectin are usually far more clinically useful.
Best practices for sample collection (sample type)
ESR is performed using whole blood collected into an EDTA tube, the same type of sample commonly used for a Full Blood Count (FBC).
The laboratory usually requires at least 1 mL of blood to perform the test accurately.
If insufficient blood is collected, the sample may be rejected.
This can occasionally happen in difficult blood draws or paediatric samples.
The Starrsed Interliner ESR analyser. A fully automated system using the Westergren ESR method.
How the analyser actually measures ESR
Modern analysers automate what used to be a completely manual process.
Tall Westergren tubes are filled with blood and left standing vertically while the analyser monitors sedimentation.
Each tube will settle differently depending on how quickly the red cells fall.
A higher ESR means the red cells have settled further down the tube.
Westergren ESR tubes. Each sample settles to a different level depending on the degree of sedimentation.
Despite looking quite primitive compared to many modern laboratory tests, ESR is still used across hospitals worldwide every single day.
Why has my doctor ordered it?
ESR is commonly requested as a general marker of inflammation.
In IBD, it is often used alongside CRP, Full Blood Count and calprotectin.
ESR can sometimes help identify ongoing chronic inflammation, particularly when monitored over time.
It is also commonly used in rheumatology conditions such as temporal arteritis and polymyalgia rheumatica.
Personally, I think ESR has fairly limited value in IBD compared with CRP and calprotectin.
What it can and cannot tell you
ESR can support evidence of inflammation, but it is very non-specific.
A raised ESR does not automatically mean active IBD.
Anaemia, pregnancy, increasing age and even some medications can affect ESR results.
This is why ESR always needs interpreting in context with symptoms and other blood tests.
- CRP and ESR both raised: stronger evidence of active inflammation
- CRP raised, ESR normal: may reflect early or acute inflammation
- ESR raised, CRP normal: may reflect chronic or resolving inflammation
IMPORTANT: ESR is often slow to rise and slow to fall. CRP usually responds much faster to changes in inflammation.
Reference ranges
ESR reference ranges vary depending on age, sex and the method used by the laboratory.
| Group | Typical Reference Range | Important Notes |
|---|---|---|
| Adult men | ~0–15 mm/hr | Often rises slightly with age |
| Adult women | ~0–20 mm/hr | Can naturally be slightly higher |
| Older adults | May be mildly elevated | Age can affect interpretation |
ESR values should always be interpreted alongside symptoms, CRP and other investigations.
Questions to ask your doctor
- How does my ESR compare with my CRP and calprotectin results?
- Could my ESR be raised for reasons unrelated to IBD?
- Are my ESR results changing over time?
- Is ESR useful for monitoring my specific condition?
- Should we repeat the test alongside other inflammatory markers?
- Would anaemia or another condition affect my ESR result?
REMEMBER: ESR is only one piece of the puzzle. Doctors interpret it alongside symptoms, scans, biopsies and other blood tests.