Evidence for abnormal regulation of circulating 1 alpha, 25-dihydroxyvitamin D in patients with pulmonary tuberculosis and normal calcium metabolism.

Available evidence indicates that hypercalcemia in pulmonary tuberculosis results from increases in circulating 1 alpha, 25-dihydroxyvitamin D [1 alpha, 25(OH)2D]. To further characterize vitamin D metabolism in this disorder, the effects of vitamin D, 100,000 units a day for 4 days, were compared in 25 normal subjects and 11 patients with active pulmonary tuberculosis who were normocalcemic and had not had hypercalcemia. Serum calcium, phosphorus, 25-hydroxyvitamin D (25-OHD) and 1 alpha, 25(OH)2D were measured. Whereas vitamin D increased mean serum 25-OHD from 20 +/- 2 (+/- SE) to 40 +/- 5 ng/ml (P less than 0.001) and did not change mean serum 1 alpha, 25(OH)2D in the normals (33 +/- 2 vs. 31 +/- 2 pg/ml), it increased mean serum 25-OHD from 21 +/- 4 to 55 +/- 13 ng/ml (P less than 0.05) and mean serum 1 alpha, 25(OH)2D from 28 +/- 2 to 35 +/- 3 pg/ml (P less than 0.05) in the patients. Serum calcium was normal and remained within the normal range in all subjects and patients. The findings indicate that there is a modest but significant abnormality in the regulation of circulating 1 alpha, 25(OH)2D in normocalcemic patients with pulmonary tuberculosis. The results are similar to those previously reported by us in normocalcemic patients with sarcoidosis.