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.

Critical illness with hyponatraemia and impaired cell membrane integrity--the "sick cell syndrome" revisited.

OBJECTIVE: To determine whether impaired cell membrane permeability exists in critically ill patients with "sick cell" type hyponatraemia. DESIGN AND METHODS: A 36 year old male patient was identified in an intensive care unit (ICU) with liver disease and multi-organ failure. His initial serum sodium (Na) was 101 mmol/L and osmolar gap + 35 mmol/L. A flow cytometric system was used to assess lymphocyte membrane integrity using fluorescein diacetate (FDA) and propidium iodide (PI). Following this, similar studies were carried out in 17 hyponatraemic (Na < 130 mmol/L) and 19 normonatraemic (Na > 136 mmol/L) ICU patients. RESULTS: Flow cytometry in the index patient showed two clear populations of cells-one was normal (with identical characteristics to a healthy control) and the other had dysfunctional cell membrane integrity. The extended patient series, however, revealed only 2 other patients with similar flow cytometric patterns-one hyponatraemic and one normonatraemic. CONCLUSIONS: Cell membrane studies in the index patient demonstrated supportive evidence for the "sick cell syndrome" in critically ill patients. The extended series revealed that 3/37 (8%) had this abnormality, which was however not consistently associated with hyponatraemia.