Which of the following tests is used to distinguish Primary Hyperparathyroidsm from Familial Benign Hypercalcemia:

Answer is C (Urinary Calcium levels): Estimation of urinary calcium excretion is the most impoant test to distinguish Familial Benign Hypercalcemia from Primary Hyperparathyroidism. Familial Hypocalciuric Hypercalcemia (also called familial Benign Hypercalcemia) overlaps mild cases of Primary Hyperparathyroidism biochemically, hormonally and clinically. PTH Concentrations do not distinguish the two disorders. Familial Hypocalciuric Hypercalcemia (also called Familial Benign Hypercalcemia) is typically associated with decreased excretion of calcium in urine while calcium excretion in urine is increased in Primary Hyperparathyroidism. Increased excretion of calcium can be estimated by 24-hour urinary calcium excretion or by the calcium creatinine clearance ratio both of which are typically decreased in Familial Benign Hypercalcemia