Determination of Reference Intervals of Some Biochemistry Tests by the Bhattacharya and Hoffmann Methods.

Background: Clinical laboratory tests are being evaluated with reference intervals (RI). Therefore, it is important that each laboratory determines and classifies its own reliable RI for each test to ensure an accurate and effective interpretation. The proposed method for determining RI is the "direct" approach, but it is a difficult, troublesome, time-consuming, and expensive method. An alternative approach is the "indirect" approach. In this study, we aimed to compare the RI values determined by the indirect method from the Calcium (Ca), Magnesium (Mg), Phosphate (P), 25-Hydroxy Vitamin D (25(OH)D), and Parathyroid hormone (PTH) test results with the RI provided by the manufacturer.

Methods: A total of 1,520,314 Ca, Mg, P, 25(OH)D, and PTH test results, which were studied in our laboratory between January and November 2022, were included in the study. Data cleaning was done for individuals between the ages of 18 - 89, and only one record was allowed. The Tukey method was used to determine and exclude extreme values. Ca and Mg tests were divided into age groups (18 - 59 and 60 - 89 years), P, 25(OH)D, and PTH tests were divided into female - male groups. RI was calculated by using the Bhattacharya and Hoffmann methods. CLIA 19 acceptable limits were used to evaluate the compliance with the manufacturer's RI.

Results: The RI results obtained by applying the Bhattacharya and Hoffmann methods were found to be significantly consistent and compatible with each other. According to the manufacturer's RI, Ca and Mg were compatible with RI in both methods, P was considered compatible with PTH and 25(OH)D upper reference limit in the Bhattacharya method, P was considered compatible with 25(OH)D lower reference limit and PTH upper reference limit in the Hoffmann method, while 25(OH)D lower reference limit was found to be different in the Bhattacharya method, and 25(OH)D upper reference limit and PTH lower reference limit were found to be different in the P male group in the Hoffmann method.

Conclusions: We believe that it is of great importance for each laboratory to determine the RI specific for the population they serve and to choose the analytical method they use according to age and gender while periodically updating them to interpret the test results correctly.