This genetic disorder (autosomal dominant inheritance with high penetrance) disrupts calcium sensing, resulting in inappropriate parathyroid hormone (PTH) release despite normal or mildly elevated serum calcium levels. The inactivating mutation affects the calcium-sensing receptors in the kidney, resulting in enhanced tubular calcium and magnesium reabsorption. Affected individuals present with typically asymptomatic hypercalcemia with normal or mildly elevated PTH levels as well as hypermagnesemia. This disorder can be distinguished from frank hyperparathyroidism by measuring urinary calcium excretion. In familial hypocalciuric hypercalcemia, urine calcium excretion is reduced, and in hyperparathyroidism, urine calcium excretion is increased.
Hyperparathyroidism secondary to renal disease – serum calcium should be normal or low, serum phosphorous should be elevated or normal, renal function should be abnormal
Hyperparathyroidism secondary to – as in or intestinal disorders that impair calcium absorption. Calcium would be normal or low, and 25-OH vitamin D will likely be low.
Lithium use (see ) – in this case, familial hypocalciuric hypercalcemia can be closely mimicked, with lowered urine calcium excretion and potentially elevated serum calcium. This will likely resolve with the withdrawal of lithium, but may not if lithium use is chronic.