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Comparison of commercially available (125)I-based RIA methods for the determination of circulating 25-hydroxyvitamin
1Departments of Pediatrics, Biochemistry and Molecular Biology, Medical University of South Carolina, 171 Ashley Ave., Charleston, SC 29425. Hollisb@musc.edu
Background:
Measurement of circulating 25-hydroxyvitamin D [25(OH)D] is important in the management of metabolic bone disease. The aim of this study was to compare two widely used methods for the quantification of circulating 25(OH)D with attention to their abilities to measure 25-hydroxylated ergocalciferol (vitamin D(2)) [25(OH)D(2)] and cholecalciferol (vitamin D(3)) [25(OH)D(3)].
Methods:
We used two commercially available, Food and Drug Administration-approved, radioiodine ((125)I)-based RIA kits for the detection of 25(OH)D (DiaSorin, Stillwater, MN and IDS Ltd, Tyne and Wear, United Kingdom). These methods were tested for general assay performance, including antibody specificity. Results were compared with those of an HPLC-based direct ultraviolet detection method.
Results:
Within- and between-run CVs were
Conclusions:
Some immunoassays may underestimate total 25(OH)D when 25(OH)D(2) constitutes an appreciable part of the total.