Abstract
To the Editor: Liquid chromatography–tandem mass spectrometry (LC-MS/MS) is becoming increasingly popular for the measurement of 25-hydroxyvitamin D [25(OH)D] in human serum. A limitation of most LC-MS/MS methods is the potential interference from coeluting isomeric compounds having identical elemental composition but different structure, leading to overestimation of true 25(OH)D concentrations. Of particular interest is the C3 epimer of 25(OH)D, 3-epi-25(OH)D, which can be present at relatively high concentrations in sera from infants, but can also be found in sera from adults, albeit at lower concentrations (1, 2). To separate 3-epi-25(OH)D from 25(OH)D, current procedures require lengthy chromatographic run times varying from 12 to 40 min (3), which makes these methods unsuitable for clinical laboratories that must deal with increasing numbers of vitamin D requests. We describe a modification of an established LC-MS/MS method for measurement of 25(OH)D3 and 25(OH)D2 (4) that allows fast separation of 25(OH)D3 from 3-epi-25(OH)D3 in human serum. Sample preparation, assay calibration, and instrument operation were carried out as described (4), with minor modifications. 25(OH)D3, 25(OH)D2, and 3-epi-25(OH)D3 were from Sigma Aldrich, and the internal standard …
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