Hypercalcemia and elevated calcitriol in a maintenance dialysis patient with tuberculosis

A patient on maintenance hemodialysis had widely disseminated tuberculosis, hypercalcemia, and elevated levels of calcitriol (1,25-dihydroxycholecalciferol). Hypercalcemia was not observed until the eighth month of hemodialysis, when persistent fevers began. At the end of a calcium-free dialysis, the plasma calcium concentration decreased to 6.6 mg/dL (1.65 mmol/L). The baseline calcitriol level was 56 pg/mL (normal, 19 to 50 pg/mL) and increased to 147 pg/mL at the end of hemodialysis. Parathyroid hormone levels by three separate assays did not appreciably increase during the hypocalcemia induced by the calcium-free hemodialysis. The serum phosphate concentration decreased from 7.3 to 4.5 mg/dL (2.36 to 1.45 mmol/L). Extrarenal production of calcitriol may occur in disseminated tuberculosis and may be stimulated by hypocalcemia and reduced serum phosphate. The expected parathyroid hormone response to hypocalcemia may have been inhibited by persistently elevated calcitriol levels or preexisting hypercalcemia.