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

Summary Available evidence indicates that hypercalcemia in pulmonary tuberculosis results from increases in circulating 1α,25-dihydroxyvitamin D [1α,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 1α,25(OH)₂D were measured. Whereas vitamin D increased mean serum 25-OHD from 20±2 (±SE) to 40±5 ng/ml (P<0.001) and did not change mean serum 1α,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<0.05) and mean serum 1α,25(OH)₂D from 28±2 to 35±3 pg/ml (P<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 1α,25(OH)₂D in normocalcemic patients with pulmonary tuberculosis. The results are similar to those previously reported by us in normocalcemic patients with sarcoidosis.