The National Institute for Health and Care Excellence recommends faecal calprotectin (f-cal) to help differentiate inflammatory bowel diseases from irritable bowel syndrome. Faecal samples for calprotectin have historically been collected at home by patients into screw-top pots and sent to laboratories where calprotectin is extracted and analysed. Faecal haemoglobin (f-Hb) samples are collected at home into specific collection devices containing stabilising buffer. We evaluated the OC-FCa method for f-cal, developed by Eiken Chemical Co., Ltd. (Japan) that uses the same collection device and analyser as f-Hb.
OC-FCa was assessed for limit of blank (LOB), limit of detection (LOD), limit of quantification (LOQ), within and between-run imprecision, linearity, prozone, recovery and carryover. A method comparison against the BÜHLMANN fCAL® turbo (BÜHLMANN Laboratories AG, Switzerland) was performed using patient samples and EQA.
The LOB was 3 µg calprotectin/g faeces (µg/g), LOD 8 μg/g and LOQ 20 μg/g. Within and between-run imprecision was <5%; linearity was good (R2 > 0.99); prozone was appropriately detected; recovery was 99.6%; no observed carryover. OC-FCa showed a strong positive bias compared with BÜHLMANN fCAL® turbo (Z=−5.3587, p < 0.001). When categorised using our local pathway, which interprets calprotectin concentrations and need for further investigation, Cohen’s Kappa demonstrates substantial agreement at <50 μg/g (κ=0.80) and >150 μg/g (κ=0.63) and fair agreement (κ=0.22) in the borderline category 50–150 μg/g.
The OC-FCa method performed well in the evaluation. With the lack of standardisation for f-cal a clinical study is required to evaluate the positive bias and establish suitable cut-off levels.
We would like to thank Eiken Chemical Co., Ltd., Tokyo, Japan and Mast Diagnostics Division, Bootle, Merseyside, UK for supplying the analysers and consumables, and UK NEQAS for providing materials for assessment.
Research funding: None declared.
Author contribution: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Competing interests: Authors state no conflict of interest.
Informed consent: Informed consent was obtained from all individuals included in this study.
Ethical approval: The local Institutional Review Board deemed the study exempt from review.
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