Stability of serum calprotectin as an emerging inflammatory biomarker: a five-day study at -20 °C and -80 °C using two analytical methods.

INTRODUCTION: Serum calprotectin is an emerging inflammatory biomarker, but data on its stability remain limited. This study aimed to determine the 5-day stability of serum calprotectin stored at 2 temperatures: ‒20 °C and ‒80 °C. METHODS: This study followed Checklist for Reporting Stability Studies recommendations using leftover serum samples. Analysis was undertaken using 2 analytical methods on an automated Siemens Atellica Solution analyzer. Twenty samples in ‒20 °C storage were analyzed using fCAL turbo reagent (BÜHLMANN), and another 10 samples in ‒20 °C storage were analyzed using GCAL reagent (Gentian Diagnostics). A further 10 patient samples stored at ‒80 °C were analyzed using fCAL turbo reagent. The maximum permissible difference was defined as total error, which was 56.43% for fCAL turbo reagent and 46.44% for GCAL reagent. RESULTS: The instability equations were y = 7.6695 × time (days) and y = 0.8553 × time (days) for temperatures of ‒20 °C and ‒80 °C, respectively, when calprotectin was determined using fCAL turbo reagent and y = 12.7011 × time (days) at ‒20 °C using GCAL reagent. DISCUSSION: Results from samples stored for a maximum of 5 days at ‒80 °C are more reliable than those stored at ‒20 °C, which may have an impact on clinical interpretation of the results.