Faecal calprotectin: comparative study of the Quantum Blue rapid test and an established ELISA method

BACKGROUND: Faecal calprotectin is a non-invasive marker for neutrophilic intestinal inflammation. It can be used in the differential diagnosis between functional and organic bowel disease. Moreover, it correlates with endoscopic organic bowel disease activity. The objective of this study is to evaluate a recently launched quantitative immunochromatographic point-of-care test: Quantum Blue Calprotectin (Bühlmann Laboratories AG, Schönenbuch, Switzerland) in comparison to an established ELISA method (Bühlmann Laboratories AG). METHODS: We included 142 samples, either archived (–80°C) faecal extracts or fresh routine samples. Both the normal range cartridges as well as the high range cartridge from the point-of-care test were used. The ELISA was compared with the point-of-care test and the optimal the point-of-care test cut-off values were searched for using Microsoft® Excel 2002 and MedCalc Software version 10.0.0.0 (Mariakerke, Belgium). RESULTS: In the method comparison a determination coefficient (R2) of 0.89 was found. The Passing Bablok regression analysis showed a significant deviation from linearity (y=–40.8+1.0x). The use of a cut-off value of 30 μg/g faeces and a grey zone of 30–110 μg/g faeces resulted in the best agreement between the ELISA interpretation and the point-of-care test interpretation, with 89.4% (127/142) agreement and 10.6% (15/142) mismatches. CONCLUSIONS: We may conclude that the point-of-care test can serve as a reliable alternative to the time consuming ELISA in the differential diagnosis between functional and organic bowel disease. Furthermore, it seems to be reliable in the follow-up of inflammatory bowel disease patients.