Interlaboratory comparison of 25-hydroxyvitamin D assays: Vitamin D Standardization Program (VDSP) Intercomparison Study 2 — Part 1 liquid chromatography – tandem mass spectrometry (LC-MS/MS) assays — impact of 3-epi-25-hydroxyvitamin D3 on assay performance

An interlaboratory comparison study was conducted by the Vitamin D Standardization Program (VDSP) to assess the performance of liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays used for the determination of serum total 25-hydroxyvitamin D (25(OH)D), which is the sum of 25-hydroxyvitamin D2 (25(OH)D2) and 25-hydroxyvitamin D3 (25(OH)D3). A set of 50 single-donor samples was assigned target values for concentrations of 25(OH)D2,...