Calprotectin, a faecal marker of organic gastrointestinal abnormality

Very different types of abnormality can give a positive faecal calprotectin test: neoplasia, IBD, infections, and the use of non-steroidal anti-inflammatory drugs.16,17 Generally, defects or increased permeability of the mucosal barrier will cause migration of large numbers of granulocytes into the intestinal lumen as a chemotactic response to the enormous number of bacteria in the bowel. By contrast, gastrointestinal bleeding of as much as 100 mL daily would be needed to increase the faecal calprotectin concentration by 6 mg/L.8 When mucosal lesions are extensive, for instance as in IBD, calprotectin concentrations are generally ten to 20 times the upper reference limit; the "unofficial world record" is 40 000 mg/L in a patient with active Crohn's disease at Aker Hospital in Oslo. The great variation in reported values in IBD (panel) is probably due to there being only a small proportion of the patients with clinical relapses. Faecal calprotectin predicts clinical relapse of IBD,17 a finding in keeping with the correlations between excretion of indium-111-labelled autologous granulocytes (r=0.8; p