Determination of fecal calprotectin reference range

Fecal calprotectin is a widely used non-invasive biomarker for the diagnosis of gastrointestinal disorders, particularly inflammatory bowel disease. However, defining reliable reference intervals is essential for accurate interpretation of test results in clinical practice. In this study, a population consisting of individuals with normal colonoscopy findings and healthy volunteers was evaluated in order to determine the reference interval of fecal calprotectin levels. A total of 115 individuals were included in the study. Outlier analysis was performed using Tukey's interquartile range (IQR) method, and data from 12 individuals were excluded based on this analysis. Thus, statistical analyses were conducted on data from 103 participants. Fecal calprotectin levels were measured using an immunoturbidimetric method, and the data were found to be non-normally distributed. Therefore, in accordance with the CLSI EP28-A3c guideline, non-parametric percentile method was applied to calculate the 2.5th and 97.5th percentiles. The resulting reference interval was determined to be 10.0–379.6 µg/g. The findings also revealed a statistically significant positive correlation between age and fecal calprotectin levels (Spearman's rho = 0.263, p < 0.05), while no significant difference was observed between sexes. Nevertheless, future studies involving larger sample sizes and the evaluation of additional parameters would be beneficial for the refinement of reference interval determinations. Key Words: Fecal calprotectin, reference interval, non-parametric method, biomarker, inflammatory bowel disease