Determination of the Reference Intervals of Clinical Biochemistry Tests by Direct and Indirect Methods: a Multicentric Study.

Background: The aim of this study was to determine the reference intervals of 14 clinical biochemistry tests in healthy individuals aged 18 - 65 years. The reference intervals determined by using direct and indirect methods were compared with each other and the manufacturer's RI in terms of gender.

Methods: Blood was collected from 302 reference subjects selected on the basis of admission and exclusion criteria based on the procedures set out in document C28-A3, and 14 clinical chemistry tests were performed using the analytical systems available in our laboratory. The analyses were conducted using the MedCalc and SPSS20 programs in the direct method and the Bellview (1.2.6 Version) program in the indirect method, according to the Bhattacharya procedure.

Results: Nine biochemical tests showed statistically significant differences according to gender (p < 0.05). These tests include alkaline phosphatase, lactate dehydrogenase, high-density cholesterol, low-density cholesterol, urea, uric acid, triglycerides, total cholesterol, and inorganic phosphate.

Conclusions: The direct method was the first method used to obtain the reference intervals. The indirect method can be used as an alternative to the direct method for AMLY and UA tests for the general population. According to the manufacturer's RI, lower and upper limits of HDL, LDL, Ca, and Mg were compatible with indirect RI in two genders. Lower and upper limits of ALP, LDH, and ALB were compatible with manufacturer's RI in female.