Tandem mass spectrometry method to measure serum 25‐hydroxy‐vitamin D concentrations for the National Health and Nutrition Examination Survey (NHANES)

Abstract

CDC has measured 25‐hydroxy‐vitamin D for NHANES using the DiaSorin RIA since NHANES III (1988‐94). Starting with NHANES 2007‐08, a tandem mass spectrometry method (LCMSMS) using a stable isotope internal standard will be used to measure 25‐hydroxy‐vitamin D2 (VID2) and 25‐hydroxy‐vitamin D3 (VID3). The method (Clin Chim Acta 2008;391:6) was recently revised to provide better chromatographic resolution, better sensitivity, and automation of sample preparation. Robotic volume delivery, robotic mixing and 96‐well plate format permit high throughput sample processing. The chromatographic run time is <10 min. Limits of detection are ≤1 ng/mL. Analytical coefficients of variation are <10% for VID3. Results for standard reference material (SRM 972) from the National Institute of Standards and Technology indicated acceptable accuracy for VID2 and VID3. Because of periodic fluctuations in long‐term quality control pools using RIA, samples from NHANES 2001‐06 are being tested using the LCMSMS method and conversion equations for LCMSMS‐RIA are being developed for each year. Samples (100/yr) were selected based on 2 criteria: 1) proportionally distributed RIA results (25 samples per unweighted quartile) and 2) an even distribution of RIA assay performance spread throughout the year. The goal of this change of methods is to improve VID assay precision. The simultaneous availability of SRM 972 will insure accuracy.