Abstract: We disclose methods for measuring vitamin D metabolite in plasma or serum samples. The methods comprise a step of adding to the plasma or serum samples a non-competitive displacement agent comprising 8-anilino-1-naphthalenesulfonic acid ammonium salt, 3-(acetonylbenzyl)-4-hydroxycoumarin and a water miscible solvent. The non-competitive displacement agent separates vitamin D metabolite from binding proteins in the sample, such that the displaced vitamin D metabolite is available for capture and detection in subsequent binding assays. Thus, our invention finds use in methods of separating and detecting vitamin D metabolites otherwise tightly bound to plasma or serum binding proteins.

Abstract: The present invention relates to a method for measuring the amount of vitamin D metabolite in a sample of plasma or serum, comprising the step of (a) adding to a serum or plasma sample a non-competitive displacement agent to effect separation of any vitamin D metabolite in the sample form protein to which it is bound, such that any vitamin D metabolite may be detected and/or measured; and (b) detecting or measuring the amount of vitamin D metabolite in the sample of (a). Such methods are useful in determining the vitamin D status of the subject, for example in the diagnosis of disease. Also provide are agents and kits for use in performing the methods of the invention.