Disorders of Calcium and Phosphate Metabolism Practice Test

FHH stems from inactivating mutations in the calcium-sensing receptor (CaSR) on parathyroid and kidney cells, which raises the set point for calcium regulation. Because the receptor is less responsive, the parathyroid glands don’t reduce PTH as much as they should at a given calcium level, and the kidneys reabsorb more calcium. The net effect is mild, often lifelong hypercalcemia with unusually low urinary calcium excretion. In practice, you’d see a low fractional excretion of calcium in the urine despite elevated serum calcium, a pattern that helps distinguish FHH from other causes of hypercalcemia that typically produce higher urinary calcium.