Normal serum 1,25-dihydroxyvitamin D in patients with medullary carcinoma of the thyroid.

Serum calcium, phosphorus, calcitonin, parathyroid hormone, 25-hydroxyvitamin D (25OHD), and 1,25-dihydroxyvitamin D [1,25-(OH)2D] were measured in 6 women and 2 men with medullary carcinoma of the thyroid, 22 normal subjects, 5 patients with chronic renal failure, and 5 patients with primary hyperparathyroidism. Serum 1,25-(OH)2D levels were significantly higher in patients with primary hyperparathyroidism and lower in patients with chronic renal failure than in normal subjects. In patients with medullary carcinoma of the thyroid, the serum calcitonin levels were elevated, but the parathyroid hormone and 1,25-(OH)2D levels were within normal ranges. The serum 25OHD levels were not significantly different in any group. It is concluded that chronic elevation of serum calcitonin has no effect on the serum 1,25-(OH)2D level.