Calprotectin Test

Fecal calprotectin (FC) is a direct marker of intestinal inflammation and one of the most clinically validated tools for evaluating diseases of the gut. It measures calprotectin, a calcium- and zinc-binding protein (S100A8/S100A9 complex), that is released from neutrophils, the immune cells that infiltrate intestinal tissue during active inflammation. Because calprotectin is highly stable in stool for several days at room temperature, it serves as a practical and non-invasive alternative to colonoscopy for assessing inflammatory bowel disease (IBD).

When intestinal inflammation occurs, neutrophils migrate into the gut mucosa and release calprotectin into the lumen, where it mixes with stool. Measuring FC provides a quantitative readout of this activity, reflecting the degree of inflammation and, indirectly, the severity of mucosal damage.

Interpreting Levels

• <50 µg/g: Normal; inflammation unlikely
• 50–150 µg/g: Borderline; mild inflammation or transient irritation possible
• >150 µg/g: Consistent with active inflammatory disease

These thresholds can vary depending on the lab and clinical context. Persistent levels above 150 µg/g often indicate active IBD, while lower or fluctuating levels may be seen in irritable bowel syndrome (IBS), infections, or use of non-steroidal anti-inflammatory drugs (NSAIDs).

Because calprotectin levels rise before clinical symptoms return, FC is particularly useful for predicting relapse in Crohn’s disease and ulcerative colitis. Studies suggest that patients in remission but with FC >150 µg/g are at significantly higher risk of relapse within 3-6 months. Conversely, declining FC levels after treatment indicate mucosal healing and successful therapy.

Clinical Use and Advantages

Fecal calprotectin offers several advantages over traditional blood-based inflammation markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), which may remain normal in localized gut inflammation. FC, by contrast, reflects local mucosal activity, making it particularly sensitive for diseases confined to the gastrointestinal tract.

• Diagnosing: Differentiating IBD from IBS in patients with chronic abdominal pain or diarrhea
• Monitoring: Assessing treatment response and mucosal healing
• Predicting relapse: Identifying early inflammatory changes before symptoms recur
• Reducing colonoscopy burden: Guiding decisions on when invasive evaluation is necessary

That said, transient increases can occur after intestinal infections, NSAID use, or heavy exercise, so results are best interpreted alongside clinical findings and follow-up testing.