Comparison of faecal calprotectin using two collection and extraction strategies for the BÜHLMANN CALEX® Cap - possible implications for clinical cut-offs?

Background: Faecal calprotectin has been identified as a useful biochemical marker in the differentiation of inflammatory bowel disease and irritable bowel syndrome. Typically, patients send faecal specimens in a pot for manual extraction by the laboratory. During the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS CoV-2) pandemic, the routine laboratory service was temporarily suspended due to the potential increased risk to staff. In this study we investigated the possibility of patients collecting samples directly into the faecal extraction tubes.

Method: Patients submitted paired faecal samples for calprotectin analysis using a standard faecal container (current practice) and followed instructions for faecal collection using the BÜHLMANN CALEX® Cap device. Samples were returned to the laboratory immediately after collection. Laboratory staff manually extracted the calprotectin from the faecal samples using the CALEX® Cap prior to analysis of both extracts on the Cobas c702.

Results: 91 paired faecal samples were included in the study. Clinical correlation was found to be 70% with numerical correlation showing a positive bias for the patient-collected CALEX® Cap sample when compared to the laboratory-extracted faecal sample around the clinical decision points 100-250 μg calprotectin/g faeces.

Conclusion: The study shows that collection of a faecal sample using the CALEX® Cap works well and is a good alternative to using standard containers. The correlation gives rise to the possibility that faecal calprotectin is not stable when collected into standard collection containers. Prior to further roll-out of this process, questions surrounding the current cut-offs would need to be addressed.