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

OBJECTIVE: Fecal calprotectin concentration in stool has recently been prop osed as a marker of colonic neoplasm and inflammation, but the intraindivid ual day-to-day variability has so far received little attention. The presen t study was undertaken to determine the biological variability of fecal cal protectin in patients referred for colonoscopy. METHODS: A prospective design was applied. In each of 14 consecutive patien ts 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 wit hin-patient variability was estimated from one-way analysis of variance. RESULTS: In absence of colonic neoplasm and inflammation, two populations o f patients emerged: one (36%) with remarkably low and stable fecal calprote ctin values all within the recommended cut-off of 50 mug/g, and one (64%) w ith labile values also beyond this limit. In this latter group, fecal calpr otectin was 70 mug/g (mean) (single tests ranged from 9 to 461), and SID wi thin patients was 52 pglg, showin- considerable day-to-day variation. Histo ry, concurrent diseases, or findings at colonoscopy could not explain labil e values. A similar pattern was observed for spot variation in one stool sa mple from healthy volunteers, suggesting that factors other than disease co ntribute to the significant intraindividual biological variation of fecal c alprotectin. 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. T he origin and pattern of fecal calprotectin excretion deserve further atten tion. (Am J Gastroenterol 2001;96:2683-2687. (C) 2001 by Am. Coll. of Gastr oenterology).