The later stages of the vitamin D deficiency syndrome during infancy are associated with impaired renal tubular reabsorption of amino acids, phosphate, and other metabolites. Secondary hyperparathyroidism has been implicated as the cause of the renal abnormality. Serum immunoreactive parathyroid hormone levels are elevated in infants with vitamin D deficiency (60 to 238 µl Eq/ml; normal < 40 µl q/ml). The highest levels were found in the more advanced stages of vitamin D deficiency.
Serum Parathyroid Hormone in X-Linked Hypophosphatemia
Serum immunoreactive parathyroid hormone (IPTH) is normal in patients with X-linked hypophosphatemic rickets who are not treated with phosphate salts. Phosphate raises IPTH in these patients. Endogenous IPTH does not influence the existing defect in tubular reabsorption of phosphate in male patients.