Evaluation of Test Standardization for 25-OH Vitamin D Immunoassays

Abstract

Background: Accurately measuring 25-OH vitamin D (25-OH-D) is important for monitoring vitamin D status. Despite the efforts of all involved parties, achieving standardization remains challenging. The present study assessed the standardization status of commercial immunoassays for measuring 25-OH-D. Methods: The diagnostic accuracy of commercial immunoassays Roche Elecsys Vitamin D Total, Siemens Atellica IM Vitamin D Total, Abbott Alinity 25-OH Vitamin D, and Beckman Coulter Access 25-OH Vitamin D Total was evaluated by comparing the quantitative values and qualitative decisions for 150 residual serums with various concentrations obtained from each test to the results determined using mass spectrometry (MS). Then, correlation and concordance were estimated. Results: When the measured 25-OH-D values from each assay were compared to those determined using MS ranging from 5.86 to 67.75 ng/mL, no evaluated immunoassay was equivalent to MS by showing slope and intercept not containing 1 and 0 in their 95% confidence interval, respectively. Regression estimates at the medical decision limits of 10, 20, and 30 ng/mL showed that only 30 ng/mL of the Beckman Coulter test was within the acceptable bias limit of 5.0% recognized by the VDSCP. The concordance of decisions with MS ranged from 90.0 to 94.0% in immunoassays. Conclusions: Despite achieving the certification by the VDSCP, most immunoassays differed significantly regarding acceptance criteria in measuring 25-OH-D, which may affect clinical decision-making. Therefore, attention should be paid to interpreting the results, and further efforts for test standardization are required.