Rickets of prematurity. Supranormal levels of serum 1,25-dihydroxyvitamin D.

Rickets, hypocalcemia, hypophosphatemia, and hyperparathyroidism were found in a low-birth-weight premature infant. The concentration of plasma calcitriol (1,25-dihydroxyvitamin D) was 145 pg/mL. With additional exogenous calcitriol (37.5 ng/kg/24 hr) given for eight weeks, the biochemical abnormalities were corrected and healing of rickets was evident. Three months later, while receiving only 400 IU of ergocalciferal daily, the patient had normal levels of serum calcium, phosphate, and alkaline phosphatase with a serum calcitriol concentration of 36 pg/mL. These observations suggest that rickets of prematurity may involve a malabsorption of calcium and phosphorus with an elevated calcitriol level needed to overcome this inadequate absorption. Additional doses of calcitriol may be of benefit in these infants, although it must be given carefully. Furthermore, the role of phosphate supplementation in these infants requires consideration.