What does a high faecal calprotectin level indicate in an acute setting?

High Fecal Calprotectin in Acute Settings: Diagnostic Significance

A high fecal calprotectin level in an acute setting strongly indicates active intestinal inflammation, particularly in patients with moderate to severe gastrointestinal symptoms, and can help guide treatment decisions without requiring immediate endoscopic assessment. 1, 2

Clinical Significance of Elevated Fecal Calprotectin

• Fecal calprotectin is a calcium- and zinc-binding protein primarily found in neutrophils, and its presence in stool directly reflects neutrophil migration into the gastrointestinal tissue due to inflammatory processes 3
• Levels >150 μg/g in patients with moderate to severe symptoms (frequent rectal bleeding, significantly increased stool frequency) reliably indicate moderate to severe endoscopic inflammation 1
• Elevated levels correlate well with intestinal inflammation severity across various conditions, making it a valuable biomarker for assessing inflammatory activity throughout the intestinal tract 2, 4

Diagnostic Accuracy in Different Clinical Scenarios

In Moderate to Severe Symptomatic Patients:

• Fecal calprotectin >150 μg/g has high positive predictive value for active inflammation, with only approximately 4.6% false positive rate in high pretest probability scenarios 1
• Can effectively rule in active inflammation and inform treatment adjustments without requiring immediate endoscopic assessment 1
• Particularly useful in ulcerative colitis where levels correlate strongly with disease activity 2, 5

In Mild Symptomatic Patients:

• Less reliable for confirming moderate to severe inflammation, with higher false positive rates (approximately 15.5% for levels >150 μg/g) 1
• Endoscopic assessment is recommended before treatment adjustment in patients with mild symptoms despite elevated calprotectin 1

Specific Conditions Associated with Elevated Fecal Calprotectin

• Inflammatory Bowel Disease (IBD): Markedly elevated in both Crohn's disease (median 31.2 mg/l) and ulcerative colitis (median 116.2 mg/l) 4
• Bacterial Infections: Significantly higher in Salmonella (median 765 μg/g) and Campylobacter (median 689 μg/g) infections compared to viral gastroenteritis 6
• Viral Gastroenteritis: Moderately elevated but significantly lower than in bacterial infections (median 89-95 μg/g for rotavirus, norovirus, and adenovirus) 6
• Colorectal Cancer: Substantially elevated (median 53.4 mg/l) compared to normal subjects 4
• NSAID-Induced Enteropathy: Shows elevated levels reflecting drug-induced intestinal inflammation 5

Clinical Application in Acute Settings

• In patients aged 16-40 with new lower gastrointestinal symptoms (>4 weeks), fecal calprotectin helps differentiate between IBD and IBS 2
• Levels correlate with clinical severity in infectious diarrhea and can help distinguish between bacterial and viral pathogens 6
• For acute flares in known IBD patients, levels >150 μg/g can guide treatment adjustments without requiring immediate endoscopy 1

Important Caveats and Limitations

• Normal calprotectin levels (<150 μg/g) in symptomatic patients do not reliably exclude inflammation, with false negative rates of 24.7% in high pretest probability scenarios 1
• NSAID use within 6 weeks can artificially elevate calprotectin levels and should be considered when interpreting results 2
• Elevated levels are not specific to any particular condition and cannot differentiate between various causes of inflammation (e.g., IBD vs. infection vs. malignancy) 4
• First morning stool samples are preferred for testing, and samples should be stored for no more than 3 days at room temperature before analysis 2

Recommended Thresholds and Interpretation

• <50 μg/g: Normal, high negative predictive value for ruling out IBD 2, 3
• 50-150 μg/g: Borderline, may warrant repeat testing or clinical correlation 2

• 150 μg/g: Significant inflammation likely, especially with moderate to severe symptoms 1

• 250 μg/g: Strong indication for urgent referral to gastroenterology in new cases 2