Vitamin D Reference Method Laboratory

CDC’s vitamin D reference method² provides highly accurate measurements of total 25-hydroxyvitamin D (25-hydroxyvitamin D2 and 25-hydroxyvitamin D3). The Joint Committee for Traceability in Laboratory Medicine (JCTLM) database lists the method as a higher-order reference measurement procedure. As such , the reference method can be used to ascertain the accuracy of commercial assays and laboratory-developed tests.

This vitamin D reference method is comparable to other reference methods, such as those used by NIST and the University of Ghent.

²Mineva EM, Schleicher RL, Chaudhary-Webb M, Maw KL, Botelho JC, Vesper HW, Pfeiffer CM. 2015. A candidate reference measurement procedure for quantifying serum concentrations of 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 using isotope-dilution liquid chromatography–tandem mass spectrometry. Anal Bioanal Chem 407(19):5615 –24.

SRM 2972a consists of two separate solutions of the vitamin D metabolites 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in ethanol. It is intended primarily for use in calibration of instruments and techniques to test for these metabolites. These solutions are prepared with a high level of accuracy. The purity of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 used to prepare these solutions is well defined. The manufacturing of the solutions is highly controlled to ensure consistency among vials and stability of the material.

Traceability in laboratory medicine describes a process used to link a patient’s results to a reference material or reference method. For vitamin D, SRM 2972a is used to calibrate a reference method. The reference method assigns reference values to serum samples. These serum samples are then used to calibrate a routine vitamin D test used to measure patient samples. In this process, measurement results for patient samples are traceable to SRM 2972a.

Establishing traceability in laboratory medicine is important because it defines the point of reference to which patient measurements are linked. This helps to ensure measurements in patient care are comparable.

The Joint Committee on Traceability in Laboratory Medicine (JCTLM) was created in 2002 through a declaration of cooperation between the International Bureau of Weights and Measures, the International Federation for Clinical Chemistry and Laboratory Medicine, and the International Laboratory Accreditation Cooperation. One of its main objectives is to promote traceability to appropriate measurement standards in ISO documents 17511, 17025, and 18153. JCTLM maintains a database with reference methods that meet the criteria mentioned in these ISO standards.