[Determination of 25-hydroxycholecalciferol in the blood by means of protein binding competition]

A competitive binding-protein assay for 25-hydroxycholecalciferol, is described in which serum from vitamin D deficient rats is used as the source of binding protein. Serum samples after extraction are chromatographed using silicic acid. Bovine albumin is used in the buffer as a protein stabilizer and lipid solubilizer, at a concentration shown to enhance the reproducibility of the assay without interfering in the binding properties of 25-hydroxycholecalciferol. The method appears to be sufficiently sensitive for clinical studies even in vitamin D deficiency.