Evaluation of a faecal calprotectin method using the OC-SENSOR PLEDIA

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.