Karin Amcoff 1, Mats Stridsberg 2, Maria Lampinen 2, Anders Magnuson 3, Marie Carlson 2, Jonas Halfvarson 1
Dept of Gastroenterology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden. 2Dept of Medical Sciences, Gastroenterology Reserarch Group, Uppsala University, Uppsala, Sweden. 3Clinical Epidemiology and Biostatistics, School of Medical Sciences, Örebro University, Örebro, Sweden.

With several fecal calprotectin (FC) assays on the market, it has been difficult to define a uniform threshold for discriminating between remission and active disease in patients with inflammatory bowel disease (IBD). We aimed to compare the results of different FC-assays in IBD patients, followed over time.

Material and Methods
IBD patients provided faecal samples and reported clinical activity every third month prospectively over a two year period. FC was measured with two ELISA- (Bühlmann and Immunodiagnostik) and one automated fluoroimmunoassay (Phadia).

In total, 13 patients provided 91 faecal samples. The absolute difference in median (IQR) concentration of FC at active disease vs. remission was higher for the Bühlmann- (845 (1061-226) µg/g vs. 62 (224-39) µg/g) than the Phadia- (369 (975-122) µg/g vs. 11 (52-11) µg/g) and the Immundiagnostik assay (135 (302-69) µg/g vs. 8 (56-4) µg/g). In contrast, the corresponding relative difference seemed to be more pronounced when analyzed by the Phadia- (ratio of means 8.5; 95% CI 3.3-21.9) or the Immundiagnostik assay (ratio of means 7.4; 95% CI 3.1-17.6) than by the Bühlmann assay (ratio 5.3; 95% CI 2.7-10.6). Consequently, the specificity for discriminating active disease from remission varied between assays (34-75%) when the cut-off 50 ug/g was used, whereas the differences in sensitivity were less pronounced.

Cross-comparisons revealed overall poor agreement between the assays as well as differences in the dynamics of FC. These findings suggest that standardization of the method is needed to implement FC as a disease monitoring tool at large-scale.