Cholecalciferol metabolites in polycythemic newborns.

Metabolites of cholecalciferol were measured in the sera of healthy and polycythemic newborns at 15.5 and 10.5 h of age (median), respectively. The serum concentrations of 1,25-dihydroxyvitamin D and 24,25-dihydroxyvitamin D were lower in the polycythemic group (P less than 0.003 and P less than 0.001, respectively). As the kidney is the main site of conversion of 25-hydroxyvitamin D to its dihydroxylated metabolites, it is possible that hyperviscosity and subsequent decrease in renal blood flow interfere with the efficiency of the process.