Radiochemical assays for vitamin D metabolites: technical possibilities and clinical applications.

Methods have been developed for the measurement of many, but not all, of the vitamin D metabolites. These methods are still laborious because of the necessity for extensive chromatographic purification but this may improve in the near future with the development of direct assays. By analogy with other steroid hormones, the production of better, and especially more specific, antibodies might be expected. In view of the numerous vitamin metabolites and isomers, chromatographic separation will however probably remain necessary for compounds present in low concentrations. The clinical usefulness of serum measurements of 25-OHD is now beyond doubt, especially since vitamin D deficiency is much more endemic than previously recognized. Measurement of 1,25-(OH)2D might also contribute to the clinical evaluation of disturbances of calcium metabolism but whether this also applies to other vitamin D metabolites awaits further research.