Calprotectin Testing: Ruling Out IBD

Reviewed and written by Dr Zeeshan Afzal, MBBS — Medical Doctor and Clinical Content Lead at Welzo. Last updated: August 2026.

If your GP has ordered a calprotectin test in the UK, it is almost always for one reason: to work out whether the symptoms you are experiencing are caused by inflammation in the bowel — as happens in Crohn's disease and ulcerative colitis — or by a non-inflammatory condition such as irritable bowel syndrome. It is one of the most useful stool tests in modern gastroenterology, and its greatest strength is not in confirming disease but in confidently ruling it out. For wider context on digestive symptoms and testing, our gut health collection and our guide to gut health in the UK are useful starting points, alongside our resources on gut barrier function, stool testing and the Bristol Stool Chart. If you are exploring supportive options while you await results, Welzo's probiotics range, Akkermansia muciniphila, Citrus Pectin Powder, Ultra Purity Berberine and Ultra Purity TUDCA are the products most often asked about in this context — none of which are a substitute for investigation. This guide explains what the test measures, how to get one on the NHS or privately, how to read your number, what can raise it other than inflammatory bowel disease (IBD), and what happens next.

Table of Contents

1. What is calprotectin?
2. What a calprotectin test UK actually measures
3. Why calprotectin is used to rule out IBD
4. IBD vs IBS: why the distinction matters
5. How to get a calprotectin test in the UK
6. How to collect the sample correctly
7. Understanding your calprotectin results
8. What else can raise calprotectin
9. What happens after a raised result
10. Using calprotectin to monitor known IBD
11. Calprotectin, FIT and blood tests compared
12. When to seek urgent medical advice
13. Frequently asked questions
14. References

What Is Calprotectin?

Calprotectin is a protein complex made of two smaller proteins, S100A8 and S100A9, that are packed inside neutrophils — the white blood cells your immune system sends to sites of active inflammation. Calprotectin accounts for a very large share of the soluble protein inside a neutrophil, with published estimates ranging from roughly 40% to 60% of the cell's cytosolic protein content. Its biological job is partly antimicrobial: it binds zinc and manganese, effectively starving bacteria of the metals they need to grow.

Structure of the calprotectin (S100A8/S100A9) complex. Image: Czeer, CC BY-SA 4.0, via Wikimedia Commons.

Why calprotectin appears in stool

When the lining of the intestine becomes inflamed, neutrophils migrate out of the bloodstream and into the bowel wall and lumen. As they degrade, they release calprotectin, which is unusually stable in faeces — it resists bacterial breakdown for several days at room temperature. That stability is what makes it practical as a posted stool test rather than something requiring an immediate hospital visit.

Crucially, the amount of calprotectin found in a stool sample correlates with how much neutrophil activity is happening in the gut. A low number means very little neutrophil traffic. A high number means something is actively drawing immune cells into the bowel lining.

Why stool rather than a blood test

Blood markers such as CRP and ESR rise with inflammation anywhere in the body — a chest infection, arthritis, a dental abscess. They are not specific to the gut, and in mild or localised bowel inflammation they are frequently normal. A faecal marker is sampled from the site itself, which is why calprotectin outperforms blood inflammatory markers for detecting bowel inflammation. Many patients still have blood work alongside it; see our overview of the gut health blood test panel for how these fit together.

The human digestive system. Calprotectin is released into the bowel lumen wherever the intestinal lining is inflamed. Image: BruceBlaus / Blausen Medical, CC BY 3.0, via Wikimedia Commons.

What a Calprotectin Test UK Actually Measures

A faecal calprotectin test measures the concentration of calprotectin in a small stool sample, reported in micrograms per gram of stool (µg/g, sometimes written mcg/g). It is a quantitative number, not a yes/no result.

How the sample is analysed

UK laboratories typically use an enzyme-linked immunosorbent assay (ELISA) or a fluorescence immunoassay. The stool sample is weighed, calprotectin is extracted using a buffer, and antibodies specific to the S100A8/A9 complex bind it so the concentration can be quantified. Some primary care networks and IBD clinics also use point-of-care devices and patient-operated home smartphone tests, which give a faster turnaround but are generally less precise at the low end.

Units, cut-offs and why UK labs differ

NICE notes that the most common cut-off recommended by test manufacturers is 50 µg/g, but that laboratories and local health economies frequently apply their own thresholds. In practice, UK pathology networks commonly use one of the following approaches:

• A single threshold of 50 µg/g, with anything above it considered abnormal
• A single threshold of 100 µg/g, adopted specifically to reduce false positives
• A three-band pathway: normal below 50, indeterminate/grey zone between 50 and 250, and clearly abnormal above 250

This is why two people with the same number can be managed differently in different parts of the country. If your result sits in a grey zone, the number on its own is far less important than the clinical picture around it. Always read your result against the reference range printed on your own report.

Why Calprotectin Is Used to Rule Out IBD

Inflammatory bowel disease is not rare. Research commissioned by Crohn's & Colitis UK and carried out at the University of Nottingham, analysing the records of 38.3 million people registered with UK GPs, found that around 0.81% of the population — approximately one in every 123 people, or more than half a million people in the UK — live with Crohn's disease or ulcerative colitis. That figure rises to about one in 67 in people over 70, and the same dataset translates to roughly 25,000 new diagnoses in 2020.

The problem is that the symptoms of IBD — diarrhoea, cramping, urgency, fatigue — are shared with far more common conditions. Sending everyone for colonoscopy is neither practical nor kind. Calprotectin exists to triage that queue.

What the evidence says about accuracy

The landmark diagnostic meta-analysis by van Rheenen and colleagues, published in the BMJ in 2010, pooled 13 prospective studies (670 adults and 371 children and teenagers). In adults, faecal calprotectin achieved a pooled sensitivity of 93% and pooled specificity of 96%. The authors calculated that screening with calprotectin would produce a 67% reduction in the number of adults requiring endoscopy. In children and teenagers, sensitivity was similar at 92% but specificity was significantly lower at 76% — an important caveat discussed below.

NICE reviewed this and other evidence in Diagnostics Guidance DG11 (2013, since renumbered as HealthTech guidance) and recommended faecal calprotectin as an option to help distinguish IBD from IBS in adults with recent-onset lower gastrointestinal symptoms in whom cancer is not suspected.

Findings from UK primary care specifically

Hospital-based accuracy figures do not automatically transfer to general practice, where the prevalence of IBD is much lower. A large UK study by Freeman and colleagues, published in BMJ Open in 2021, analysed 5,970 adults in UK primary care who had a first calprotectin test. At the 50 µg/g threshold the results were:

The same study found that raising the threshold from 50 to 100 µg/g missed fewer than 7% of additional IBD cases — which is precisely why several UK pathology services have moved to the higher cut-off.

The difference between ruling out and diagnosing

Those two numbers — 99.6% negative predictive value and 8.1% positive predictive value — tell the whole story. Calprotectin is an excellent rule-out test and a poor rule-in test. A normal result is genuinely reassuring. A raised result is a prompt for further thought, not a diagnosis. NICE's own NHS adoption resource documented local experience suggesting roughly 30% of raised results in some settings were false positives, which is why a single elevated number should never be interpreted in isolation.

IBD vs IBS: Why the Distinction Matters

Irritable bowel syndrome is a disorder of gut–brain interaction. It is real, it can be disabling, and it does not cause structural damage or measurable neutrophilic inflammation in the bowel wall. Inflammatory bowel disease does, and it can lead to strictures, fistulas, hospital admission, surgery and an increased long-term risk of bowel cancer if untreated.

Where the symptoms overlap

The British Society of Gastroenterology's 2021 IBS guidelines recommend that everyone presenting with IBS-type symptoms for the first time in primary care has a full blood count, CRP or ESR, coeliac serology, and — in patients under 45 with diarrhoea — a faecal calprotectin to exclude inflammatory bowel disease. If you would like more on the IBS side of that picture, see our guides to the different types of IBS, supplements for IBS in the UK and the low FODMAP diet. Coeliac disease is a separate exclusion — see coeliac testing in the UK and coeliac vs gluten intolerance.

Endoscopic view of ulcerative colitis: loss of the normal vascular pattern with granular, friable mucosa. Image: Samir, CC BY-SA, via Wikimedia Commons.

Red flag symptoms that override a normal result

A normal calprotectin does not cancel out alarm features. Seek prompt medical review — regardless of your test number — if you have visible rectal bleeding, unintentional weight loss, a persistent change in bowel habit over the age of 50, an abdominal or rectal mass, unexplained iron-deficiency anaemia, or a strong family history of bowel cancer or IBD. Our guide on when to see a GP about stomach symptoms covers this in detail, as does our explainer on bowel cancer screening in the UK.

How to Get a Calprotectin Test in the UK

Through the NHS

The usual route is via your GP. If your symptom pattern fits the NICE and BSG criteria — persistent lower gastrointestinal symptoms, typically with diarrhoea, without features suggesting cancer — your GP can request a faecal calprotectin through the local pathology laboratory. You are given a small collection kit to use at home and return it, usually to the surgery or directly to the lab. Turnaround is commonly one to two weeks, though this varies considerably by region.

Uptake has grown steadily but unevenly. A companion study using the same UK primary care database found 19,840 calprotectin tests recorded across 17,027 patients between 2006 and 2016, with two-thirds of practices having started testing by 2016 — and noted that only a small minority of tests were preceded by symptoms that met the eligibility criteria, suggesting the test is often used more broadly than intended.

Private and home testing

Private laboratory and postal calprotectin tests are widely available in the UK. They typically involve a home collection kit, prepaid return postage, and a quantitative laboratory result with a doctor's comment. Costs generally sit in the region of £40 to £100 depending on the provider and whether a clinician review is included.

A private test can be useful if you face a long wait, if you want to track a known trend, or if you simply want information. Two honest caveats: first, a private raised result still needs NHS or specialist follow-up, because the definitive next step is endoscopy; second, testing without a clinical assessment risks both false reassurance and unnecessary anxiety. If you are weighing up broader testing options, compare our guides to gut microbiome testing, microbiome test comparisons, food intolerance testing and zonulin testing — the last of which is far less clinically established than calprotectin.

How to Collect the Sample Correctly

Sample quality genuinely affects the number. NHS trusts issue broadly consistent instructions:

1. Do not contaminate the sample with urine or toilet water. Place clean toilet paper, a clean container, or the supplied collection sheet across the toilet bowl first.
2. Use the spoon or probe in the lid to transfer a small amount — usually about a teaspoon, or enough to fill the marked line on a probe device.
3. Take the sample from a formed part of the stool where possible. Watery stool dilutes calprotectin, and stool consistency is known to influence the measured value.
4. Label the pot clearly with your name, date of birth and the date and time of collection.
5. Return it promptly. Follow the lab's storage instructions — many ask you to refrigerate the sample if it cannot be posted or delivered the same day.
6. Tell your clinician about recent illness or medication, especially anti-inflammatory painkillers, antibiotics or a recent bout of gastroenteritis.

You do not need to fast, change your diet, or stop most medications beforehand. Recording your stool type using the Bristol Stool Chart at the time of collection is genuinely helpful for whoever interprets the result.

The Bristol Stool Chart. Stool consistency influences faecal calprotectin values, so noting your stool type is useful. Image: Cabot Health, Bristol Stool Chart, CC BY-SA 3.0, via Wikimedia Commons.

Understanding Your Calprotectin Results

The table below reflects the banding used across many UK primary care pathways. Your own laboratory's reference range takes precedence.

What a normal result means

With a negative predictive value around 99% in UK primary care, a result under 50 µg/g in someone without red flag symptoms makes IBD very improbable. That is a meaningful piece of information: it usually means you can move on to managing the symptoms themselves rather than chasing further invasive tests. Many people in this position are dealing with IBS, bile acid malabsorption, lactose intolerance, SIBO or diet-related bloating — see foods that cause bloating and supplements for bloating.

What a borderline result means

Grey-zone results are common and frequently transient. UK primary care pathways typically advise reviewing possible contributors — anti-inflammatory painkillers, proton pump inhibitors, recent gastroenteritis — and repeating the test after several weeks. A number that falls back into the normal range on repeat is reassuring; one that rises warrants referral.

What a high result means

A clearly raised result indicates active neutrophilic inflammation somewhere in the intestine. IBD is the most important cause to exclude, but it is not the only one. What a high number does not tell you is where the inflammation is, what is causing it, or how severe the underlying disease is. That requires direct visualisation.

What Else Can Raise Calprotectin Besides IBD

Medicines

Non-steroidal anti-inflammatory drugs (ibuprofen, naproxen, diclofenac, aspirin) can cause low-grade damage to the intestinal lining and are the best-recognised cause of a falsely raised calprotectin — see our article on ibuprofen and stomach damage. Proton pump inhibitors have also been associated with higher values: a 2025 observational study of 431 patients with functional bowel disorders found median calprotectin of 66 µg/g in those with a recent PPI prescription versus 23 µg/g in those without. Our guide to long-term omeprazole effects covers this class in more depth. Recent antibiotics may also raise levels indirectly through changes in the gut microbiome; see probiotics after antibiotics.

Infections and other gut conditions

Bacterial, viral and parasitic gastroenteritis all raise calprotectin, sometimes dramatically, and levels can take weeks to settle after the illness has passed — see recovering from a stomach bug. Other non-IBD causes include coeliac disease, microscopic colitis, diverticulitis, Clostridioides difficile infection, colorectal polyps and colorectal cancer. H. pylori-related upper gastrointestinal disease is a less consistent contributor.

Age, exercise and other factors

Calprotectin is naturally high in newborns and falls towards adult levels by around four to five years of age, which is why paediatric interpretation differs and why the standard 50 µg/g reference performs poorly in children. One published paediatric cohort found that 76% of children referred for suspected IBD purely on the basis of a raised calprotectin above 50 µg/g did not have IBD. Values also tend to drift up with older age, and strenuous endurance exercise can produce a temporary rise — relevant reading in our guides to gut health for athletes and runner's trots.

What Happens After a Raised Result

Repeat testing

For borderline and moderately raised values in someone who is otherwise well, most UK pathways recommend removing reversible causes and repeating the test after around six weeks. This single step avoids a substantial number of unnecessary referrals.

Colonoscopy and biopsy

Where the result is high, or where symptoms are progressive, referral to gastroenterology follows. Colonoscopy with biopsies of the terminal ileum and each colonic segment remains the reference standard for diagnosing IBD. Small bowel imaging — MR enterography or capsule endoscopy — may be added if Crohn's disease is suspected beyond the reach of the colonoscope.

Colonoscopy allows direct inspection and biopsy of the bowel lining. Image: Cancer Research UK, CC BY-SA 4.0, via Wikimedia Commons.

Serpiginous ulceration in the colon of a patient with Crohn's disease. Image: Samir, via Wikimedia Commons.

If a diagnosis of IBD is confirmed, treatment is led by a specialist team and may include aminosalicylates, corticosteroids for flares, immunomodulators and biologic therapies. Diet is supportive rather than curative — see our guides to the Crohn's disease diet and the ulcerative colitis diet. Any supplement use in IBD, including probiotics, should be discussed with your IBD team first; our article on probiotic safety explains why.

Using Calprotectin to Monitor Known IBD

Once IBD is diagnosed, calprotectin changes role. It becomes a non-invasive way to track disease activity, assess response to treatment and detect a flare — sometimes before symptoms return. A meta-analysis of calprotectin for assessing IBD activity reported pooled sensitivity of 92% and specificity of 60% at a 50 µg/g cut-off, 84% and 66% at 100 µg/g, and 80% and 82% at 250 µg/g; the area under the curve was higher for ulcerative colitis than for Crohn's disease.

In practice, IBD teams often use serial measurements rather than single values. A number that has doubled from your personal baseline matters more than whether it crossed an arbitrary line. Many patients are asked to test every three to six months while stable, and more often during treatment changes.

Calprotectin, FIT and Blood Tests Compared

FIT and calprotectin answer different questions and are frequently requested together. NICE's guidance on quantitative FIT (DG56) notes that GPs are likely to order a calprotectin test alongside FIT, since calprotectin is the more accurate test for IBD. Neither replaces the other.

When to Seek Urgent Medical Advice

Contact your GP urgently, or seek same-day care, if you experience:

• Significant or persistent rectal bleeding
• Severe abdominal pain, particularly with fever
• Six or more bloody bowel motions in 24 hours, with fever or a fast heart rate
• Unintentional weight loss
• Persistent vomiting or an inability to keep fluids down
• Symptoms of anaemia — breathlessness, marked fatigue, palpitations

These features require assessment regardless of any stool test result.

Supporting Your Gut While You Wait for Results

None of the following treats or diagnoses IBD, and none should delay investigation. But while you are waiting, the evidence-supported basics are worth attention: a diverse, largely whole-food diet, adequate fibre, regular sleep and managed stress. Our guides to eating 30 plants a week, the best foods for gut health, short-chain fatty acids and microbiome diversity cover the underlying science. If you are considering supplements, read how to choose a probiotic in the UK and whether probiotics work first, and speak to your clinician — particularly if inflammation has been confirmed.

Frequently Asked Questions

What is a normal calprotectin level in the UK?

Most UK laboratories treat a faecal calprotectin below 50 µg/g as normal, though a number of pathology services use 100 µg/g as their threshold to reduce false positives. Always check the reference range printed on your own report, because it varies by laboratory and assay.

Can you have IBD with a normal calprotectin?

It is possible but uncommon. In UK primary care the negative predictive value at 50 µg/g was 99.6%, meaning fewer than one in 200 people with a normal result went on to be diagnosed with IBD. Isolated small bowel Crohn's disease is the situation most likely to produce a normal or only mildly raised result, so persistent or worsening symptoms should always be reassessed.

How much does a private calprotectin test cost in the UK?

Private postal calprotectin tests in the UK generally cost somewhere between £40 and £100, depending on the provider, turnaround time and whether a doctor's interpretation is included. On the NHS the test is free when requested by your GP.

How long do calprotectin results take?

NHS laboratory results typically take one to two weeks, though this varies considerably between regions. Private postal tests often report within two to five working days of the sample reaching the laboratory. Point-of-care devices can give a result in under an hour but are less precise.

Does a high calprotectin always mean Crohn's or colitis?

No. In UK primary care only around 8% of raised results at the 50 µg/g threshold corresponded to a subsequent IBD diagnosis. Anti-inflammatory painkillers, proton pump inhibitors, recent gastroenteritis, coeliac disease, diverticulitis, polyps and colorectal cancer can all raise the number. A raised result means further assessment is needed, not that you have IBD.

Do I need to stop ibuprofen before a calprotectin test?

NSAIDs are a well-recognised cause of raised calprotectin, and many UK pathways suggest stopping them where clinically safe before a repeat test. Do not stop any prescribed medication without speaking to your GP or pharmacist first — but do tell whoever ordered the test that you have been taking them.

Can stress or anxiety raise faecal calprotectin?

There is no good evidence that psychological stress alone produces a meaningfully raised faecal calprotectin. Stress can worsen IBS symptoms considerably through the gut–brain axis without causing the neutrophilic inflammation that calprotectin measures — which is one reason the test is so useful for separating the two.

What calprotectin level indicates a colonoscopy is needed?

There is no single national number. Many UK pathways refer for consideration of colonoscopy above 250 µg/g, repeat testing between roughly 50 and 250 µg/g, and manage below 50 µg/g in primary care. Symptoms, age, red flags and blood results all influence the decision alongside the number.

How often should calprotectin be checked in known IBD?

This is decided by your IBD team. Many patients in stable remission are tested every three to six months, with more frequent testing around treatment changes, after surgery, or when symptoms alter. Trends over time are more informative than any individual value.

Is calprotectin testing accurate in children?

It is useful but less specific. The pooled specificity in children and teenagers was 76%, compared with 96% in adults, and levels are naturally high in infancy before settling by around four to five years of age. Paediatric results should always be interpreted by a clinician familiar with age-appropriate reference ranges rather than against adult cut-offs.

References

1. National Institute for Health and Care Excellence. Faecal calprotectin diagnostic tests for inflammatory diseases of the bowel (DG11). https://www.nice.org.uk/guidance/dg11
2. National Institute for Health and Care Excellence. DG11 — The diagnostic tests (cut-off values). https://www.nice.org.uk/guidance/dg11/chapter/4-the-diagnostic-tests
3. National Institute for Health and Care Excellence. DG11 adoption support resource: insights from the NHS. View resource
4. van Rheenen PF, Van de Vijver E, Fidler V. Faecal calprotectin for screening of patients with suspected inflammatory bowel disease: diagnostic meta-analysis. BMJ 2010;341:c3369. https://pubmed.ncbi.nlm.nih.gov/20634346/
5. Freeman K, Taylor-Phillips S, Willis BH, Ryan R, Clarke A. Test accuracy of faecal calprotectin for inflammatory bowel disease in UK primary care. BMJ Open 2021;11:e044177. https://pmc.ncbi.nlm.nih.gov/articles/PMC7903095/
6. Freeman K, Ryan R, Parsons N, et al. Faecal calprotectin testing in UK general practice. British Journal of General Practice 2021;71(712):e854–e861. https://bjgp.org/content/71/712/e854
7. Vasant DH, Paine PA, Black CJ, et al. British Society of Gastroenterology guidelines on the management of irritable bowel syndrome. Gut 2021;70:1214–1240. Read the guideline (PDF)
8. Crohn's & Colitis UK. New research shows over 1 in 123 people in the UK living with Crohn's or Colitis. Read the release
9. Crohn's & Colitis UK / University of Nottingham. Epidemiology summary: incidence and prevalence of IBD in the United Kingdom. Read the summary (PDF)
10. Lab Tests Online UK. Calprotectin. https://labtestsonline.org.uk/tests/calprotectin
11. University College London Hospitals NHS Foundation Trust. Faecal calprotectin test — patient information. Read the patient information
12. Royal United Hospitals Bath NHS Foundation Trust. Faecal calprotectin pathway for primary care (PATH-013). View the pathway (PDF)
13. Nie B, et al. Meta-analysis: faecal calprotectin for assessment of inflammatory bowel disease activity. Inflammatory Bowel Diseases 2014. https://pubmed.ncbi.nlm.nih.gov/24983982/
14. Prescription of NSAIDs and proton pump inhibitors are associated with increased faecal calprotectin levels in patients with functional bowel disorder. Scandinavian Journal of Gastroenterology 2025. https://pubmed.ncbi.nlm.nih.gov/40438967/
15. Guidance on the interpretation of faecal calprotectin levels in children. PLOS ONE / PMC. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7877663/
16. National Institute for Health and Care Excellence. Quantitative faecal immunochemical testing to guide colorectal cancer pathway referral in primary care (DG56). Committee discussion

About the Author

Dr Zeeshan Afzal, MBBS is a practising medical doctor and the Clinical Content Lead at Welzo. He reviews Welzo's digestive health content for clinical accuracy against current UK guidance from NICE, the British Society of Gastroenterology and the NHS. This article was researched and written by Dr Afzal and is reviewed on a rolling 12-month cycle, or sooner if national guidance changes.

Medical Disclaimer

This article is for general information and education. It is not a substitute for individual medical advice, diagnosis or treatment from a qualified healthcare professional. Faecal calprotectin results must be interpreted alongside your symptoms, examination and other investigations. Do not start, stop or change any prescribed medication on the basis of this article. If you have symptoms that concern you, contact your GP; if you are acutely unwell, contact NHS 111 or attend your nearest emergency department. Welzo does not diagnose or treat inflammatory bowel disease, and no supplement is a treatment for IBD.