American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the daily urinary calcium level for diagnosing familial hypercalciuric hypocalcemia?

1. 50 mg

2. 80 mg

3. 100 mg

4. 150 mg

The correct answer is: 100 mg

The daily urinary calcium level that is indicative of familial hypercalciuric hypocalcemia typically exceeds 100 mg. This condition is characterized by elevated serum calcium levels and low serum parathyroid hormone levels along with high urinary calcium excretion, which can be used to differentiate it from other calcium-related disorders. In familial hypercalciuric hypocalcemia, the urine calcium is often significantly elevated due to the renal handling of calcium being altered, leading to increased calcium excretion despite low serum calcium. The threshold of 100 mg per day is an important cutoff in diagnosing this condition, as urinary calcium levels at or above this point strongly suggest familial hypercalciuric hypocalcemia. Values below this threshold are generally not consistent with the diagnosis and may suggest other potential causes of hypercalcemia or low urinary calcium levels unrelated to this familial condition. Hence, the correct choice is supported by the need for significant urinary calcium levels indicative of the disorder.