Disorders Of Calcium And Phosphate Metabolism Practice Test

Hypercalcemia in granulomatous diseases is driven by macrophage-driven production of active vitamin D outside the kidney, which increases intestinal calcium absorption. Activated macrophages within granulomas express 1α-hydroxylase and convert circulating 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (the active hormone) regardless of PTH levels. This extra calcitriol raises calcium absorption from the gut, pushing serum calcium upward. Because calcium is high, PTH is suppressed, and the hypercalcemia is not due to PTH-driven renal reabsorption or calcitonin changes. Vitamin D status plays a crucial distinction here: deficiency would reduce, not increase, calcium absorption, so it cannot explain hypercalcemia in this context. Treatment focuses on reducing macrophage activity (often with glucocorticoids) and addressing the underlying granulomatous process to limit extrarenal calcitriol production.