A test was developed to diagnose various forms of hypercalciuria. A two-hour urine sample after an overnight fast and a four-hour urine sample after 1 g of calcium by mouth were tested for calcium, cyclic AMP and creatinine. The 24 patients with absorptive hypercalciuria had normocalcemia and normal fasting urinary calcium (< 0.11 mg per milligram of urinary creatinine). Urinary calcium was high (≥ 0.2 mg per milligram of creatinine) after a calcium load. Of the 28 patients with primary hyperparathyroidism (resorptive hypercalciuria), 25 had hypercalcemia and 21 had high fasting urinary calcium. Urinary cyclic AMP, elevated in 30 per cent of fasting patients, was high (> 4.60 μ moles per gram of creatinine) in 82 per cent of cases after calcium load. Six patients with renal hypercalciuria had normocalcemia, high fasting urinary calcium, and high (> 6.86 μ moles per gram of creatinine) or high-normal fasting urinary cyclic AMP. After a calcium load, urinary cyclic AMP was normal. This simple test should facilitate the differentiation of various causes of hypercalciuria. (N Engl J Med 292:497–500, 1975), MANY causes have been implicated for the formation of calcium-containing renal stones. The most common one is probably the hypercalciuria associated with normocalcemia. Previously called idiopathic hypercalciuria,.
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