Verification of fCAL turbo Buhlmann reagent for determining serum calprotectin

The aim of this study was to verify Buhlmann fCAL turbo reagent, used for analysing calprotectin in stool, on serum samples.

Leftover patients' serum samples were used. Verification protocol included: precision performed in accordance with Clinical and Laboratory Standards Institute (CLSI) EP15-A3 guidelines; comparison of Buhlmann fCAL turbo and serum GCAL Gentian reagents; verification of reference intervals (RI) proposed from literature (0.68-5.45 mg/L) in accordance with CLSI EP28-A3C guidelines; limit of blank (LoB) and limit of quantitation (LoQ) performed in accordance with CLSI EP17-A2 guidelines; linearity performed in accordance with CLSI EP6-A guidelines; carry-over and lastly, hook effect. Acceptance criteria were based on manufacturer specifications stated in the package insert for the fCAL turbo Buhlmann reagent designed for analysing calprotectin in stool samples.

The CVs% for precision were within acceptance criteria, ≤10 %. Bland-Altman analysis showed the presence of a bias of 3.4 mg/L (95 % confidence interval 2.00-4.79). The equation for the Passing-Bablok regression was y= -0.01 (-0.08 to 0.06) + 0.37 (0.36-0.40)x, and it showed proportional difference. The obtained LoB was 0 mg/L, while the LoQ was 0.04 mg/L (CV% ≤ 20 %). The method was linear in the range 0.04-4.14 mg/L, and carry-over (0.1 %) and hook effect were not detected. The proposed RI in the literature was verified using 20 leftover patients' samples.

Despite being declared for analysing stool samples only, Buhlmann fCAL turbo reagent can be used to determine serum calprotectin. Buhlmann fCAL turbo reagent is not comparable to the GCAL Gentian reagent.