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P278. Clinical comparison of eight different calprotectin immunoassays for the diagnosis and follow-up of inflammatory bowel disease

D. Labaere1, A. Smismans1, G. Van Olmen2, P. Christiaens2, G. D'Haens2, V. Moons2, P.-J. Cuyle2, J. Frans1, P. Bossuyt2, 1Imelda general hospital Bonheiden, Laboratory Medicine, Bonheiden, Belgium, 2Imelda general hospital Bonheiden, Gastroenterology, Bonheiden, Belgium

Background

Fecal calprotectin (FC) may be of value as a marker for diagnosis and follow-up of inflammatory bowel disease (IBD). Instead of the time-consuming ELISA, newer fast and/or automated tests have been developed. We prospectively evaluated the performance of 8 different calprotectin assays for the diagnosis of IBD and for monitoring disease activity in ulcerative colitis (UC) and Crohn's disease (CD).

Methods

33 patients with suspected IBD and 31 IBD patients in follow-up provided a stool sample for calprotectin measurement. We determined FC by means of 3 point-of-care tests (POCT) (Bühlmann Quantum Blue, Eurospital Calfast, Biotest Certest), 4 ELISA's (Bühlmann, Eurospital, Calpro and Calprolab) and 1 fully automated immunoassay (Phadia). Results were compared with endoscopic and histological findings.

Results

After adjusting the optimal cut-off by ROC-curve analysis, sensitivity and specificity for diagnosis of IBD were comparable for the different assays, and ranged from 82 to 83% and from 84 to 89%, respectively. The discriminatory power to distinguish IBD from non-IBD appeared highest for the Bühlman Quantum Blue, Phadia and the Calprolab assay, with ratios of median IBD/non-IBD calprotectin values of respectively 14, 12 and 10.

For monitoring of disease activity, the semi-quantitative Certest was omitted because no acceptable combination of sensitivity and specificity could be reached at its fixed cut-off. For the other assays, mild UC (Mayo score 1) could be differentiated from remission with a sensitivity of 71–100%. In moderate to severe UC (Mayo 2–3), sensitivity was 100% for all assays. Specificity ranged from 67 to 86% in both subgroups.

In CD patients, only disease activity with a SES-CD (Simple Endoscopic Score for Crohn's Disease) above 7 could be differentiated from remission, with a sensitivity of 83–86%, and a specificity of 75% for all tests. Although all methods correlated significantly, the slopes and/or intercepts differed extensively.

Conclusion

All calprotectin assays showed acceptable and comparable clinical performance for diagnosis of IBD. For follow-up of known IBD, performance of the different assays was moderate to good, except for mild Crohn's disease, which is difficult to differentiate from remission. The ELISA's can be safely replaced by their corresponding quantitative POCT assays.

Based on the inter-test disagreement, one cannot compare trial results or multiple results from one patient, if they are obtained with a different assay.