Analytical and clinical validation of a radioimmunoassay for the measurement of 1,25 dihydroxy vitamin D

Objectives: The analytical and clinical validation of the DiaSorin 1,25 dihydroxyvitamin D RIA is described. Design and Methods: The analytical parameters assessed included analytical sensitivity, dilution linearity, intra- and inter-assay precision, recovery, specificity, and interference studies. Where appropriate, assessments were performed according to NCCLS guidelines. The clinical validation assessed normal individuals and end-stage renal disease patients. Results: The analytical sensitivity of the assay is < 2.0 pg/mL or < 4.8 pM. The assay is specific for both 1,25 dihydroxyvitamin D2 and D3. Recovery ranged from 97% to 108% for spiked samples. Intra-assay precision, as %CV, ranged from 7% to 11%, while inter-assay precision was 12% to 15%. No interference was observed from bilirubin, cholesterol, hemoglobin, or triglycerides. Clinical validation demonstrated complete discrimination between normal and ESRD populations. Conclusions: These data demonstrate that the DiaSorin 1,25 (OH)2 vitamin D RIA is a robust, accurate, and precise tool for the assessment of 1,25 (OH)2 vitamin D.