3-epi-25 hydroxyvitamin D concentrations are not correlated with age in a cohort of infants and adults

Background: The implementation of mass spectrometry to measure serum 25-hydroxyvitamin D [25(OH)D] concentrations has led to concerns regarding the measurement and reporting of the C3-epimer of 25-hydroxyvitamin D-3[3-epi-25(OH)D-3], for which there is a near-total lack of data regarding its clinical significance. Methods: We developed a chromatographic method to resolve (>90%) 3-epi-25(OH)D-3 from 25(OH)D-3 using a pentafluorophenyl propyl chromatographic column. Using LC-MS/MS, we determined the serum concentrations of 25(OH)D-3 and 3-epi-25(OH)D-3 in 626 patients aged 3 days to 94 years undergoing routine vitamin D testing. Results: Comparison between DiaSorin RIA and the new LC-MS/MS method for total 25(OH)D had acceptable agreement. Our data indicate an increase in 25(OH)D-3 rather than a reduction in epimer concentration. An average of 3.3 ng/ml of 3-epi-25(OH)D-3 was detected in adolescents and adults. Inclusion of 3-epi-25(OH) D-3 in the total 25(OH)D-3 concentration resulted in 9% (<1 year) and 3% (1 to 94 years) potential misclassification of patients as vitamin D sufficient. Conclusions: The new LC-MS/MS method is capable of chromatographically separating 25(OH)D-3 and 3-epi-25(OH)D-3. It was used to confirm that the contribution of 3-epi-25OHD(3) to total 25OHD(3) concentrations decreases with age in infants and is detectable in adults. (C) 2011 Elsevier B.V. All rights reserved.