Plasma concentrations of vitamin D metabolites in a case of rickets of prematurity.

Rickets was diagnosed in an extremely low-birthweight infant 16 weeks after birth. She had a normal plasma concentration of 25-hydroxyvitamin D, a relatively low level of 24,25-dihydroxyvitamin D, and a markedly elevated 1,25-dihydroxyvitamin D level compared with adult standards. The plasma concentrations of the vitamin D metabolites were, however, indistinguishable from those of healthy preterm infants who received a similar diet of human milk and vitamins. The results indicate that rickets was not caused by vitamin D deficiency or by abnormal vitamin D metabolism, but by calcium and/or phosphate deficiency, and that the calcium and phosphorous content of human milk may be inappropriately low for very low-birthweight infants.