An assessment of 25-hydroxyvitamin D measurements in comparability studies conducted by the Vitamin D Metabolites Quality Assurance Program

• Published in: Clinica chimica acta 2013-11, Vol.426, p.6-11
• Main Authors: Bedner, Mary, Lippa, Katrice A., Tai, Susan S.-C.
• Format: Article
• Language: English
• Subjects: 25-Hydroxyvitamin D; Humans; Immunoassay; Interlaboratory comparison; Liquid chromatography; Mass spectrometry; Quality assurance; Quality Assurance, Health Care; Vitamin D - analogs & derivatives; Vitamin D - blood; Vitamin D - metabolism
• ISSN: 0009-8981; 1873-3492
• DOI: 10.1016/j.cca.2013.08.012

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health Office of Dietary Supplements, established the first accuracy-based program for improving the comparability of vitamin D metabolite measurements, the Vitamin D Metabolites Quality Assurance Program. The study samples were human serum or plasma Standard Reference Materials (SRMs) with 25-hydroxyvitamin D values that were determined at NIST. Participants evaluated the materials using immunoassay (IA), liquid chromatography (LC) with mass spectrometric detection, and LC with ultraviolet absorbance detection. NIST evaluated the results for concordance within the participant community as well as trueness relative to the NIST value. For the study materials that contain mostly 25-hydroxyvitamin D3 (25(OH)D3),the coefficient of variation (CV) for the participant results was consistently in the range from 7% to 19%, and the median values were biased high relative to the NIST values. However, for materials that contain significant concentrations of both 25-hydroxyvitamin D2 (25(OH)D2) and 25(OH)D3, the median IA results were biased lower than both the LC and the NIST values, and the CV was as high as 28%. The first interlaboratory comparison results for SRM 972a Vitamin D Metabolites in Human Serum are also reported. Relatively large within-lab and between-lab variability hinders conclusive assessments of bias and accuracy. •VitDQAP, the first accuracy-based program for 25(OH)D, used serum SRMs as study samples.•Summary statistics were determined for LC, immunoassay, and all method results.•Participant performance was consistent for SRMs containing mostly 25(OH)D3.•Participant immunoassay results were biased low for serum SRMs with high 25(OH)D2.•In general large within- and between-lab variability hindered accuracy assessments.