Fecal Calprotectin Test: What High Levels Mean

What is Fecal Calprotectin?

I see patients in my clinic every week who have been struggling with chronic abdominal pain, bloating, and erratic bowel habits. For many, the worry is inflammatory bowel disease (IBD) such as Crohn’s disease or ulcerative colitis. One of the most valuable, non-invasive tools I reach for is the fecal calprotectin test. It’s a protein released by white blood cells in the gut lining when inflammation is present. Measuring it in a stool sample helps me distinguish between active inflammation and functional disorders like irritable bowel syndrome (IBS).

Why is the Test Done?

Fecal calprotectin is predominantly used to screen for and monitor IBD. It helps avoid unnecessary colonoscopies in patients with low risk, and it can signal disease flare-ups in those already diagnosed. My patients often ask, “Can you just tell from symptoms?” Unfortunately, diarrhoea and pain overlap between IBD and IBS. Calprotectin provides objective evidence of gut inflammation. It’s also employed to assess response to treatment, especially in children and young adults where repeated endoscopy is invasive.

How is the Test Performed?

The process is straightforward. You collect a small sample of stool (about the size of a walnut) in a dedicated container, ideally on two separate days from different bowel movements. The LOINC code for this parameter is 59659-0 (Calprotectin [Mass/volume] in Stool). The sample is sent to a lab where an immunoassay quantifies calprotectin. No special preparation is needed, but it’s wise to avoid NSAIDs like ibuprofen for a week before, as they can falsely elevate levels. The test is reliable, safe, and non-invasive — a big relief for my patients who are anxious about colonoscopy.

Normal Reference Ranges for Fecal Calprotectin

Reference values can vary slightly between laboratories, but the widely accepted thresholds are consistent across age groups. The table below shows the typical interpretation used in major gastroenterology guidelines.

Note: Some labs use a single cut-off of 50 µg/g for adults. Levels above this warrant further investigation, though a mild elevation (50–120) can also be seen in non-steroidal anti-inflammatory drug use or gastrointestinal infections.

What Do Elevated Levels Mean?

High fecal calprotectin indicates neutrophilic inflammation in the intestinal mucosa. The most common causes are:

• Inflammatory bowel disease (Crohn’s disease, ulcerative colitis)
• Infectious colitis (bacterial, viral, parasitic)
• Non-steroidal anti-inflammatory drug (NSAID) enteropathy
• Colorectal cancer (though less common)
• Severe diverticulitis

Importantly, functional disorders like IBS do not elevate calprotectin. In my practice, a normal result in a symptomatic patient is very reassuring and steers management toward diet, stress reduction, and gut-directed therapies rather than immunosuppressants.

Fecal Calprotectin in Crohn’s Disease vs Ulcerative Colitis

Both conditions cause elevated levels, but the magnitude can differ. Ulcerative colitis, which involves continuous inflammation of the colon, often produces higher calprotectin values (frequently >500–1000 µg/g). Crohn’s disease, which can be patchy and affect the small bowel, may show moderately elevated levels, sometimes in the 150–500 µg/g range. However, there is considerable overlap — the test cannot reliably distinguish between the two. That’s where imaging and colonoscopy with biopsies remain essential.

Can Fecal Calprotectin Differentiate IBD from IBS?

Yes, this is one of its strongest applications. A landmark meta-analysis showed that a cut-off of 50 µg/g has a sensitivity of 89% and specificity of 81% for distinguishing IBD from IBS. In other words, a normal calprotectin makes IBD very unlikely. I often tell my patients: “If your calprotectin is below 50, we can be more than 90% confident that you do not have active inflammation.” This can save months of worry and avoid unnecessary scopes.

Factors That Can Affect Results

False-positive elevations aren’t rare. Common culprits include:

• Use of NSAIDs (e.g., ibuprofen, naproxen) — can cause low-grade gut inflammation
• Acute gastroenteritis — will raise calprotectin transiently
• Recent colonoscopy with biopsies — wait at least 2 weeks after the procedure
• Stool contamination with urine or water — ensure proper collection

I always ask my patients about medications and recent illnesses before interpreting results. A single mildly elevated value (50–120 µg/g) should prompt a repeat test after addressing these factors, rather than rushing to colonoscopy.

What Happens if My Levels Are High?

An elevated calprotectin is not a diagnosis — it’s a signpost. The next step typically involves:

1. Repeat testing to confirm, especially if the value is borderline.
2. Stool cultures to rule out infection.
3. Calprotectin monitoring over time to see trends.
4. Colonoscopy with biopsies if levels are persistently high and clinical suspicion remains.

Don’t panic. Many conditions that raise calprotectin are treatable. The test helps us focus the diagnostic workup and avoid unnecessary procedures. In my experience, the relief patients feel when a normal result rules out IBD is palpable — it often transforms their anxiety into a constructive plan for managing IBS or other functional symptoms.

Limitations of Fecal Calprotectin

No test is perfect. Fecal calprotectin cannot:

• Localise the exact site of inflammation
• Differentiate between types of IBD
• Detect inflammation in the upper GI tract (e.g., eosinophilic oesophagitis)
• Rule out microscopic colitis (which often requires biopsy)

Moreover, levels can be normal in some cases of mild Crohn’s disease, especially if the disease is in the small bowel. That’s why calprotectin is best used in combination with clinical assessment, inflammatory markers (CRP, ESR), and imaging when needed.