Potential pitfalls of the 2-hour calcium-to-creatinine ratio and urinary cyclic adenosine monophosphate excretion in the differential diagnosis of idiopathic hypercalciuria.

We studied 44 patients with calcium urolithiasis on high (900 mg. daily) and low (400 mg. daily) calcium diets. With 24-hour urinary data, we categorized the patients as normocalciuric or hypercalciuric and subdivided the hypercalciuric patients into absorptive and renal types. Abbreviated tests, including the 2-hour fasting urinary calcium-to-creatinine ratio and 24-hour urinary (nephrogenous) cyclic adenosine monophosphate, did not predict accurately whether hypercalciuria was of the idiopathic, absorptive or renal type. However, 24-hour urinary calcium excretions on the low calcium diet had a sensitivity and specificity of more than 90 per cent for reproducing the categorized diagnoses.