Fecal calprotectin in clinical practice: a noninvasive screening tool for patients with chronic diarrhea.

Background: Surrogate markers of colorectal inflammation are increasingly being recognized as important in differentiating organic from functional intestinal disorders. Fecal calprotectin (FC) can be easily measured in the stool, being released by leukocytes in inflammatory conditions.

Aim: We evaluated FC as an index of inflammation in consecutive outpatients referred for colonoscopy for chronic, nonbloody diarrhea.

Methods: Stool specimens of 346 outpatients with chronic, nonbloody diarrhea, referred for colonoscopy, were measured for FC levels. The proportion of patients correctly diagnosed with the test and the relationship with endoscopic and histologic findings were measured.

Results: Abnormal endoscopic findings were detected in 104 patients (30.1%). Histologic findings included 142 patients (41.0%) with inflammation and 204 (59.0%) without inflammation. Fecal excretion of calprotectin significantly correlated with the finding of inflammation at endoscopy and histology (P<0.0001). When 150 mcg/g of stool was used as the upper reference limit, FC showed 75.4% sensitivity and 88.3% specificity, with 81.7% positive and 83.7% negative predictive values for histologic inflammation.

Conclusions: In outpatients referred for colonoscopy a measurement of FC is accurate to identify those with histologic inflammation. Assay of FC may be a reliable and noninvasive screening tool to identify inflammatory causes of chronic, nonbloody diarrhea.