Measurement of 24,25 dihydroxyvitamin D in sera of neonates and children.

Serum concentration of 25OHD and 24,25(OH)2D were measured in lipid extracts of serum by competitive radioassay following separation of the metabolits by Sephadex LH-20 column chromatography. The concentration of 24,25(OH)2D in children and adolescents (3.3 +/- 1.3 SD ng/ml) was significantly greater (P less than 0.01) than the levels recorded in neonates (1.8 +/- 0.6 ng/ml), and was approximately one-tenth the concentration of 25OHD in the two populations (children 35.2 +/- 9.2 ng/ml; neonates 14.4 +/- 3.4 ng/ml, P less than 0.01). Although 24,25(OH)2D is present in significant quantities in the sera of children and adolescents, its metabolic function remains unknown at present.