Determination of reference intervals of complete blood count tests in adult individuals by indirect method

Introduction: Reference intervals are of critical importance in the comparison of laboratory measurements and the medical decision-making process, serving as the most common and essential tool in this context. Each laboratory should establish and periodically reevaluate reference intervals specific to its measurement methods and local population. Objectives: The aim of this study was to determine the reference intervals for complete blood count test parameters analyzed in our hospital laboratory using the indirect method, based on patient results recorded in the laboratory information system. Methods: Complete blood count test results obtained in our laboratory between 2015 and 2023 were transferred to an Excel program. A data filtering process was applied to exclude inappropriate results, and preliminary data cleaning was performed. Outliers were eliminated using the Tukey method. The Harris-Boyd method was employed to determine whether reference intervals should be stratified by gender. To establish reference intervals for complete blood count parameters using the indirect method, nonparametric, Bhattacharya, ReflimR, Kosmic and RefineR approaches were applied. A verification process was conducted to assess the usability of the determined reference intervals. Results: Significant differences was found between males and females for RBC, HB, HTC, MCH, MCHC, PLT, MO%, MO# and PCT tests, leading to the establishment of gender-specific reference intervals. It was observed that the use of different indirect techniques significantly affected the reference intervals. In the verification process, the reference intervals obtained for all parameters using all methods were deemed valid. The reference intervals provided by the manufacturer did not fully reflect the reference values specific to our regional population. Comparisons with other studies revealed differences in reference values. Conclusion: Differences in reference intervals among studies have been attributed to various factors, including the sampling methods for reference individuals, characteristics of the reference population (such as ethnicity, nutritional status, regional altitude and lifestyle), measurement methods, the autoanalyzers used and the statistical approaches applied in determining reference intervals. To reduce these discrepancies, standardization and harmonization are of paramount importance in both direct and indirect reference interval studies. In our study, reference intervals determined using the Kosmic and RefineR methods produced the most consistent results compared to other approaches, aligning closely with both the directly obtained values in our laboratory and findings reported in the literature. We recommend the use of novel indirect methods such as Kosmic and RefineR in place of the traditional nonparametric and Bhattacharya approaches, which are frequently used in indirect reference interval studies. In the coming years, as more experience is gained with indirect methods, we believe these techniques will become more valuable and may eventually replace the direct method. Key words: Complete Blood Count, Reference İntervals, Indirect Method, Nonparametrik, Bhattacharya, ReflimR, Kosmic, RefineR