Hypercalciuria

Hypercalciuria is a medical condition in which there is an abnormally high amount of calcium excreted in the urine. It is commonly defined by a 24-hour urinary calcium excretion above the upper limit of normal, with a typical adult threshold around 300 mg per day, though reference ranges can vary by age and laboratory method. Many individuals are asymptomatic, while others may develop kidney stones or nephrocalcinosis. The condition can be primary (idiopathic) or secondary to another disorder, and a distinct entity called familial hypocalciuric hypercalcemia features low urinary calcium despite elevated blood calcium.

Classification and causes

Primary or idiopathic hypercalciuria is the most common form and often has a genetic predisposition. Secondary hypercalciuria occurs with conditions that raise calcium in the blood or change renal handling, such as hyperparathyroidism, excessive vitamin D intake or disorders of vitamin D metabolism (eg, sarcoidosis), renal calcium leak from other tubular defects, or prolonged immobilization. Medications can influence calcium excretion; thiazide diuretics reduce urinary calcium, while loop diuretics increase it. Familial hypocalciuric hypercalcemia is characterized by high blood calcium with relatively low urinary calcium.

Pathophysiology and risk

The excess urinary calcium may result from increased intestinal absorption, altered bone turnover, or impaired renal reabsorption of calcium. Associated factors include low urinary citrate and dietary influences (high sodium intake raises calciuria). Stone formation and nephrocalcinosis are the main complications; bone health may be affected in some patients.

Evaluation and management

Evaluation includes measurement of serum calcium, parathyroid hormone, 25-hydroxyvitamin D, renal function, and a 24-hour urinary calcium (or spot calcium-to-creatinine ratio). Distinguishing idiopathic hypercalciuria from secondary causes and from familial hypocalciuric hypercalcemia guides management. Treatment emphasizes adequate hydration, normal calcium intake, reduced sodium intake, and, in recurrent stone formers, measures such as potassium citrate or thiazide diuretics. Addressing underlying conditions and monitoring bone health are also important. Prognosis varies with underlying cause and adherence to management.