Analytical performance and diagnostic accuracy of six different faecal calprotectin assays in inflammatory bowel disease

Background: We evaluated the analytical performance of six different faecal calprotectin immunoassays together with their diagnostic accuracy in the discrimination between functional and organic bowel disorders. Methods: The faecal samples were obtained from inflammatory bowel disease patients (n = 27) at the time of diagnosis [Crohn's disease (n = 15), colitis ulcerosa (n = 12)], gastroenterologic disease control patients (n = 52) and rheumatologic disease control patients (n = 26). All individuals included in the study underwent a concurrent ileocolonoscopy. Analytical performance (imprecision, accuracy, carry-over, correlation and agreement) and diagnostic accuracy (sensitivity, specificity, likelihood ratios) of the different assays were evaluated. Results: All methods demonstrated good analytical performance, but within-run and total imprecision varied depending on the assay methodology used. Using Passing Bablok and Bland-Altman analyses, low quantitative agreement was observed between the assays. All assays showed excellent diagnostic accuracy, with areas under the receiver operating characteristic curves (ROC) ranging from 0.974 to 0.998. The AUCs were not significantly different between assays (p > 0.05). Diagnostic sensitivity at the cut-off at a fixed specificity of 75% ranged from 95.2% to 100%. Introduction of multiple result intervals increased the clinical interpretation of all the assays. Conclusions: Analytical and diagnostic performance of the evaluated faecal calprotectin assays is good, but numerical values differ substantially between the assays necessitating the use of different clinical cut-offs. Introduction of multiple result intervals aids in clinical decision-making.