Comparative study of fecal calprotectin (FC) rapid test with the established ELISA method

Background. FC is a useful marker for diagnosing inflammatory bowel disease (IBD). However, no automated assay is available yet and widely adopted ELISA methods show turnaround time of≥4h. We compared the point of care (POC) Quantum Blue FCimmunochromatographic test (Buhlmann) to the Calprest ELISA (Eurospital) routinely used in our laboratory. Methods. Stool specimens of 67 consecutive patients were analyzed after extraction using recommended device. FC was determined on fresh samples by POC, while for the ELISA stool samples were frozen at -20 °C, and thawed, extracted, and assayed within 2 weeks from collection. We first compared results by Passing Bablok regression and then estimated diagnostic agreement by adopting 90 μg/g feces as cut-off for ELISAand an experimentally recalculated cut-off for POC. Results. Method comparison, performed on 28 paired results higher than the POCdetection limit(30 μg/g), showed a slope of 2.24 (ELISA in x-axis), with not significant intercept. On the basis of this finding, the POC cut-off was established at 200μg/g. FC was positive on 20 samples by ELISA and on 17 samples by POC, with a 92.5% agreement. Among fivepatients showing discrepant results, 4 were positive on ELISA (two borderline – 94 and 98 μg/g – results) and one positive on POC. This POC “false-positive” related to a 16-years old girl, with chronic diarrhea but no IBD diagnosis. Conclusions. Our preliminary results suggest that POC may replace the standard ELISA and make FC testing more rapid (<20 min), effective, and suitable for any laboratory setting.