Vitamin D deficiency causes rickets, requiring vitamin D at doses greater than daily dietary intake. Several treatment regimens are found in the literature, with wide dosing ranges, inconsistent monitoring schedules, and lack of age-specific guidelines. We describe 3 children, ages 2 weeks to 2 and 9/12 years, who recently presented to our institution with hypercalcemia and hypervitaminosis D (25-hydroxyvitamin D levels >75 ng/mL), associated with treatment of documented or suspected vitamin D-deficient rickets. The doses of vitamin D used were within accepted guidelines and believed to be safe. The patients required between 6 weeks and 6 months to correct the elevated serum calcium, with time to resolution of hypercalcemia related to age and peak serum calcium, but not to peak 25-hydroxyvitamin D level. With recent widespread use of vitamin D in larger dosages in the general population, we provide evidence that care must be taken when using pharmacologic dosing in small children. With limited dosing guidelines available on a per weight basis, the administration of dosages to infants that are often used in older children and adults has toxic potential, requiring a cautious approach in dose selection and careful follow-up. Dosage recommendations may need to be reassessed, in particular, where follow-up and monitoring may be compromised.

The annual number of Pex in pediatric CF patients is significantly associated with 25-OHD levels and gender, raising the consideration that maintaining vitamin D sufficiency may lead to decreased incidence of Pex and hospitalizations requiring antibiotic therapy.

Delay in diagnosis of hyperparathyroidism is common in children, related to vague symptomatology and infrequent use of laboratory evaluations in children. Such delays lead to increased risk of osteoporotic fractures and kidney stones. This case illustrates the emergent need of diagnostic evaluation in children presenting with similar symptoms. We emphasize the importance of bone densitometry in children, which is not often considered as part of the standard evaluation in this age group. The remarkable increase in bone mineral density in the 1 yr after surgery attests to the plasticity of recovery of the growing skeleton.