Analytical validation of the Roche 25-OH Vitamin D Total assay

Background: Vitamin D deficiency is considered a major health issue and therefore there is a need for reliable routine tests for measurement of the vitamin in blood samples. Here we present a validation of the recently released Roche 25-OH Vitamin D Total assay (Vitamin D Total). Methods: We analyzed control materials (2 levels) and patient serum pools (3 levels) ranging from 34 to 123 nmol/L 84 times over a period of 21 days, and we analyzed five serum pools in 10 separate runs to verify the limit of quantification. We also analyzed 53 paired samples of serum and Li-heparin plasma. We evaluated the 25-OH Vitamin D Total assay in comparison to our in-house liquid chromatography tandem mass spectrometry (LC-MS/MS) method [194 patient samples without 25-hydroxy vitamin D-2 (25OHD(2)) and 23 patient samples containing 25OHD(2)]. Results: At concentrations of 34 and 56 nmol/L within-run CVs were 4.8% and 1.9% and total CVs were 8.3% and 6.1%. We verified that the limit of quantification was 22.5 nmol/L, as stated by the manufacturer. No significant difference was observed between serum and plasma samples (Li-heparin). Comparison with LC-MS/MS using 194 samples containing 25OHD(3) only (no 25OHD(2)) showed Vitamin D Total nmol/L=1.07x(LC-MS/MS) nmol/L+4.7 nmol/L, whereas comparison of 25OHD(2) using 23 patient samples showed Vitamin D Total nmol/L=0.55x(LC-MS/MS) nmol/L-2.38 nmol/L (Demings regression). Conclusions: The Roche Vitamin D Total assay is judged suitable for measurement of 25OHD in serum and Li-heparin plasma. Results for 25OHD(3) are comparable to those obtained by LC-MS/MS, while results for 25OHD(2) are around half of those obtained by LC-MS/MS.