Biological variability of fecal calprotectin in patients referred for colonoscopy without colonic inflammation or neoplasm

OBJECTIVE: Fecal calprotectin concentration in stool has recently been proposed as a marker of colonic neoplasm and inflammation, but the intraindividual day-to-day variability has so far received little attention.The present study was undertaken to determine the biological variability of fecal calprotectin in patients referred for colonoscopy. METHODS: A prospective design was applied. In each of 14 consecutive patients submitted for colonoscopy, eight stool samples were collected before the endoscopy. A detailed questionnaire was used. Calprotectin was measured by quantitative enzyme-linked immunoassay, and standard deviation for the within-patient variability was estimated from one-way analysis of variance. RESULTS: In absence of colonic neoplasm and inflammation, two populations of patients emerged: one (36%) with remarkably low and stable fecal calprotectin values all within the recommended cut-off of 50 μ/g, and one (64%) with labile values also beyond this limit. In this latter group, fecal calprotectin was 70 μ/g (mean) (single tests ranged from 9 to 461), and SD within patients was 52 μ/g, showing considerable day-to-day variation. History, concurrent diseases, or findings at colonoscopy could not explain labile values. A similar pattern was observed for spot variation in one stool sample from healthy volunteers, suggesting that factors other than disease contribute to the significant intraindividual biological variation of fecal calprotectin. CONCLUSIONS: Day-to-day variation of fecal calprotectin is considerable in patients without colonic inflammation or neoplasm, for whom the pattern of stabile low fecal calprotectin may seem to be a valid negative predictor. The origin and pattern of fecal calprotectin excretion deserve further attention.