Abstract
IntroductionWe assessed the differences in faecal calprotectin (FC) concentrations measured by two assays depending on the stool consistency and extraction method.Materials and methodsStool samples were extracted using the EliA Stool Extraction Kit, Calex® Cap extraction device and respective weighing methods, while FC concentrations were measured using the EliATM Calprotectin and Bühlmann fCAL® Turbo method and checked for within- and between-method variability with regard to extraction method and stool consistency category. Extraction yield was evaluated for impact of different sample incubation time (10 min and 1 h) in extraction buffer for both methods and for impact of different initial sample dilutions (1:50, 1:100, 1:500) for fCAL® Turbo method.ResultsResults determined from Calex® Cap extracts were higher compared to weighing method extracts (mean bias 33.3%; P < 0.001), while no significant difference was found between results obtained with EliA Stool Extraction Kit and weighing method (mean bias 0.1%; P = 0.484), in both cases irrespective of stool consistency. Bühlmann fCAL® Turbo results were higher than EliATM Calprotectin results (mean bias 32.3%, P = 0.025 weighing method; and mean bias 53.9%, P < 0.001 extraction devices), the difference is dependent on stool consistency and FC concentration. Significantly higher FC extraction yield was obtained with longer sample incubation time for both methods (P = 0.019 EliATM Calprotectin; P < 0.001 fCAL® Turbo) and with increasing initial sample dilution for fCAL® Turbo method (P < 0.001).ConclusionPreanalytical stool sample handling proved to be a crucial factor contributing to within- and between-FC assay variability. Standardization is urgently needed in order to assure comparable and reliable FC results.
Highlights
We assessed the differences in faecal calprotectin (FC) concentrations measured by two assays depending on the stool consistency and extraction method
Study included only the leftovers of stool samples consecutively submitted to our laboratory for routine Faecal calprotectin (FC) determination, no additional samples were requested from patients
Median FC concentration in Calex extracts was significantly higher (P < 0.001) in comparison to weighing method extracts with calculated mean bias of 33.3%, which exceeded acceptable criteria
Summary
We assessed the differences in faecal calprotectin (FC) concentrations measured by two assays depending on the stool consistency and extraction method. Faecal calprotectin (FC) is a stable, feasible biomarker, which is released in stool through neutrophilsdisruption during inflammation in bowel mucosa. Its determination substantially reduces the need for invasive endoscopy with biopsy which is expensive but regarded as gold standard for assessing mucosal inflammation [1,2]. The lack of overall process standardization, from faecal sample preparation to methodology used for FC measurement, results in great variability between commercially available assays [7,8,9,10,11]. As the gold standard FC extraction method, is rather impractical and time-consuming; extraction devices have been introduced as convenient alternative [12].
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