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P087. Comparative study of the Quantum Blue rapid test for point of care quantification of faecal calprotectin with an established ELISA method

L. Coorevits1, F. Baert2, H. Vanpoucke1

1H. Hart Ziekenhuis Roeselare-Menen VZW, Laboratory, Roeselare, Belgium; 2H. Hart Ziekenhuis Roeselare-Menen VZW, Gastro-enterology, Roeselare, Belgium

Background: Faecal calprotectin (FC) has proven its utility as a non-invasive marker for neutrophilic intestinal inflammation. It can be used in the differential diagnosis between functional and organic bowel disease. In Crohn's disease and ulcerative colitis, FC is a very useful biomarker as it correlates with endoscopic disease activity. The objective of this study is to evaluate the recently launched quantitative immunochromatographic point of care tests (POCT) (Quantum Blue Calprotectin, Bühlmann Laboratories AG) to the currently used ELISA method (Bühlmann Laboratories AG) both numerically and regarding its reliability in distinguishing functional from organic bowel disease.

Methods: 142 samples were analysed both with the ELISA and the POCT (normal range (30–300 µg/g faeces) or high range (100–1800 µg/g faeces) cartridge). Manufacturer's instructions were strictly followed. During the previous in-house evaluation of the ELISA, a cut-off value of 50 µg/g faeces and a grey zone of 50–200 µg/g faeces were established. These values were revised with the POCT, in order to interpret the results of both methods clinically as similar as possible. Different cut-off values were derived using ROC analysis and applied to the measurement results. The analogy of interpretation was judged by means of the % agreement and the % mismatches. In addition, a determination coefficient was calculated using 127 samples (20 samples were excluded because of the lack of an exact test value (out of range)).

Results: We found a determination coefficient of 0.89. Regarding the clinical interpretation, a cut-off of <30 µg/g faeces to rule out inflammation and >110 µg/g faeces to confirm inflammation (grey zone of 30–110 µg/g faeces) were found to be the most suitable for the POCT. This resulted in 89.4% (127/142) agreement and 10.6% (15/142) mismatches with the ELISA test. Of those mismatches 93.3% (14/15) concerned minor errors (negative or positive result vs. grey zone result) and only one was a major error (false negative result). This false negative result could not be avoided without resulting in a significant loss of sensitivity.

Conclusions: We conclude that the POCT can serve as a reliable alternative to the time consuming ELISA, using a cut-off value of 30 µg/g faeces and a grey zone of 30–110 µg/g faeces in the differential diagnosis between functional and organic bowel disease. Overall, the POCT (normal and high range) shows a good correlation with the ELISA test.