ThreeCommercial KitsandOne Liquid-Chromatographic MethodEvaluated forDetermining 25-Hydroxyvitamin D3in Serum

The accuracy of three commercial kit methods and one Iiquid-chromatographic (HPLC) methodfor determining25hydroxyvitamin 03 in serum was evaluated by usingisotope dilution-massspectrometryas a referencetechnique.The kit methodswere basedon radioimmunoassay and radioreceptor assay. Serum samples were analyzed from male and female volunteers, some of whom had been exposed to ultravioletB lightor givenvitaminD3orally.Resultsobtained withthe three commercialkitswere lessaccuratethan those by HPLC. The agreement between the HPLC method and the comparisonmethodwas relativelygood: r = 0.99; slope = 1.23: intercept = -2.9 zg/L. We concludethat methods