I Analyse Your Stool for a Living (and I Have UC). Let’s Talk Calprotectin.

All about Faecal Calprotectin:

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.

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.

Rathan than directly attacking them, it starves them. A strategy known as “nutritional immunity.”

1. 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.

1. 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 Run Faecal Calprotectin 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.

Faecal Calprotectin ELISA reagents. Boxes and boxes of these line our cold room!

We use an automated analyser called the DYNEX® DS2 ELISA system. It’s not the most complicated analyser, or the biggest, but this baby will set you back around £100,000 if you want one!

If you think your poo smells, imagine 100 other people just like us. So yeah, we use a fume cupboard to pull that smell away from our nostrils and into the lovely fresh Manchester air. 

Result Interpretation:

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!

• The median value in healthy adults is 25µ/g (mg/kg)
• Samples with a calprotectin concentration < 50 µg/g are regarded as negative.
• Samples with a calprotectin concentration between 50 µg/g and 100 µg/g are regarded as borderline positive. We recommend repeating the measurement at a later time point in order to confirm the result.
• Samples with a calprotectin concentration > 100 µg/g are regarded as positive.

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:

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. 

 

Thanks for reading,I really hope it's useful and interesting. It’s a long one, took me a long time to write, but honestly Faecal Cal deserves it! 

It will never replace a colonoscopy when needed, but it serves a really important part of our repertoire of diagnostic tools for IBD. I'm incredibly grateful for the NHS providing it as a service from a personal and professional perspective. 

You keep sending. I’ll keep testing.

Take care, and all the best on your IBD journey.

Chris