What is the role of stool calprotectin (fecal calprotectin) in diagnosing and managing inflammatory bowel disease (IBD)?

Role of Stool Calprotectin in Diagnosing and Managing Inflammatory Bowel Disease

Stool calprotectin is a validated biomarker for intestinal inflammation that plays a crucial role in both diagnosing inflammatory bowel disease (IBD) and monitoring disease activity, serving as a non-invasive alternative to endoscopy in appropriate clinical scenarios. 1

Diagnostic Role in Suspected IBD

Initial Evaluation Algorithm

1. For patients aged 16-40 with lower GI symptoms >4 weeks:

   • Measure fecal calprotectin if IBD is suspected
   • Interpretation thresholds:
     • <100 μg/g: IBS likely, treat in primary care
     • 100-250 μg/g: Consider repeat testing or routine referral to gastroenterology

     • 250 μg/g: Refer urgently to gastroenterology 1

2. Important caveats:

   • Not appropriate if NSAIDs used in past 6 weeks (can cause false elevations)
   • Not sensitive enough for excluding colorectal cancer
   • Patients with rectal bleeding, change in bowel habit, weight loss, or iron deficiency anemia should be referred via suspected cancer pathway regardless of calprotectin level 1

Diagnostic Performance

• Best sensitivity (90.6%) at 50 μg/g cutoff
• Best specificity (78.2%) at levels >100 μg/g 1, 2
• Higher specificity (82%) at threshold of 250 μg/g 1
• Better performance in ulcerative colitis than Crohn's disease (AUC 0.91 vs 0.84) 2

Role in Monitoring Disease Activity

Assessment of Disease Activity

• Validated biomarker for endoscopic and histological disease activity 1
• Correlates well with endoscopic inflammation in both ulcerative colitis and Crohn's disease 1
• Useful when unclear if new symptoms represent relapse or other causes 1
• More reliable than clinical indices and serum markers in assessing mucosal inflammation 3

Predicting Disease Course

• Elevated levels in patients in clinical remission predict increased risk of relapse within 12 months 3
• Can detect subclinical mucosal inflammation in clinically quiescent IBD 3
• Helps identify patients at risk for relapse 3

Practical Considerations

Sample Collection

• Use first stool passed in the morning
• Store for no more than 3 days at room temperature before analysis 1
• Patient self-testing options now available (e.g., CalproSmart) with good correlation to lab ELISA testing (correlation coefficient 0.685) 4

Interpretation Challenges

• Different assays may have varying results between laboratories
• Remains elevated for weeks after infectious gastroenteritis
• Can be elevated in other conditions including colorectal cancer 5
• Interpretation must always consider the clinical context 6

Clinical Pitfalls to Avoid

1. Don't rely solely on calprotectin for cancer exclusion

   • Not sensitive enough for colorectal cancer; patients with concerning symptoms need cancer pathway referral regardless of calprotectin level 1, 5

2. Don't measure if unnecessary

   • If relapsing disease is clinically obvious, measurement is not necessary 1

3. Don't interpret in isolation

   • Always interpret in context of pre-test probability of IBD
   • If strong suspicion of IBD (clinical features or family history), refer even with intermediate values 1

4. Don't forget confounding factors

   • NSAIDs can cause elevated levels 1, 6
   • Bacterial infections can cause very high calprotectin levels 6

Fecal calprotectin represents a significant advance in non-invasive IBD assessment, providing valuable information for both diagnosis and monitoring while reducing the need for invasive procedures in appropriate clinical scenarios.