Indirect estimation of serum enzymes reference intervals in adults using the reflimR and refineR algorithms.

Introduction: Many clinical laboratories rely on manufacturer-provided reference intervals (RIs) because of logistical and financial constraints of direct RI estimation. Indirect estimation methods offer a practical alternative for deriving RIs from laboratory data. This study aimed to estimate RIs for eight serum enzymes using the R-based algorithm reflimR, and to compare them with refineR, manufacturer's instructions for use (IFU), and direct methods. Materials and methods: Data from adult outpatients tested between January 2021 and May 2022 were retrospectively analyzed for alkaline phosphatase (ALP), alanine aminotransferase (ALT), amylase, aspartate aminotransferase (AST), creatine kinase (CK), gamma-glutamyl transferase (GGT), lactate dehydrogenase and lipase. Reference intervals were estimated using reflimR and refineR, and compared with IFU and direct RIs. Overlap between lower and upper limits was evaluated using a color-coded scheme. Data distribution was tested with Shapiro-Wilk; and Mann-Whitney U and Spearman's correlation tests were used for group comparisons and correlations. Results: Sex-specific RIs were required for ALP, ALT, AST, CK and GGT. ReflimR generally produced wider intervals than refineR. Agreement of reflimR with refineR, parametric, and IFU-based RIs was 88.5%, 72.7%, and 62.5%, respectively. The lowest agreement was observed with the non-parametric method (55.0%). Conclusions: ReflimR provides a practical approach for indirect RIs estimation from routine data. Its performance was comparable to refineR and parametric methods, supporting its use for verifying or updating local RIs, especially where population-specific RIs are unavailable. To our knowledge, this is the first study to apply reflimR to the Turkish population and directly compare its performance with refineR and IFUs.