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Total calcium in urine
Last reviewed: 05.07.2025
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In metabolic equilibrium, the daily excretion of calcium in the urine corresponds to the absorption of calcium in the intestine. The excretion of calcium in the urine depends on the amount of calcium filtered in the glomeruli and tubular reabsorption. Ionized calcium and calcium in complex with low-molecular anions (approximately 60% of the total amount in the blood serum) are filtered in the glomeruli. The kidneys reabsorb 87-98% of the filtered calcium. Calcium reabsorption occurs passively in the entire nephron. The proximal convoluted tubules reabsorb 60%, the loop of Henle - 30%, the distal part of the nephron - 10% of calcium. Calcium reabsorption in the distal tubules of the kidneys is stimulated by PTH. For a complete picture of calcium metabolism in the patient's body, it is necessary to study it in the urine.
Reference limits for total urinary calcium excretion
Diet |
Number of Sa |
|
Mg/day |
Mmol/day |
|
Lack of calcium in the diet Calcium intake below average Average calcium intake (800 mg/day or 20 mmol/day) |
5-40 50-150 100-300 |
0.13-1 1.25-3.75 2.5-7.5 |
Normal mechanisms of calcium homeostasis prevent hypercalcemia by increasing urinary calcium excretion. Therefore, any nonrenal increase in serum calcium increases calcium filtration and urinary calcium excretion. Increased sodium delivery to the loop of Henle and distal renal tubules (eg, with furosemide) also increases urinary calcium excretion. Hypercalciuria results from impaired calcium reabsorption anywhere in the nephron. Understanding these mechanisms has important implications for the treatment of nephrolithiasis associated with hypercalciuria.