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The causes of increased and decreased calcium in the urine
Last reviewed: 19.10.2021
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Hypercalciuria - urinary excretion of more than 300 mg / day calcium in men and more than 250 mg / day in women, or more accurately - the release of calcium in the urine in an amount of more than 4 mg / kg of ideal body weight per day in either sex.
Calcium stones account for 70-80% of all kidney stones. Approximately 40-50% of patients with calcium stones observe hypercalciuria. In 40% of these patients idiopathic hypercalciuria is detected, 5% - primary hyperparathyroidism, 3% - renal-calcium acidosis. Other causes of hypercalciuria include excessive intake of vitamin D, calcium and alkali, sarcoidosis, Itenko-Cushing syndrome, hyperthyroidism, Paget's disease and immobilization.
Elevated calcium excretion in the urine is observed with hypercalcemia associated with malignant neoplasms, osteoporosis, dysfunction of the proximal tubules, the use of diuretics (furosemide, ethacrynic acid).
Most often, with kidney stones, idiopathic hypercalciuria is detected. This heterogeneous disorder associated with increased release of calcium in the urine with intestinal hyperabsorption (absorbent hypercalciuria) or reduced reabsorption of calcium in the renal tubules (loss through the kidneys). Absorptive hypercalciuria is possible with primary intestinal anomaly with hyperabsorption due to increased intestinal reactivity to calcitriol (type I) or elevated calcitriol in blood (type II). An increase in the concentration of calcitriol may cause loss of phosphate through the kidneys, which in the future will cause a decrease in inorganic phosphorus in the blood serum, increased production of calcitriol, increased intestinal calcium absorption, increased serum calcium and hypercalciuria (type III). The primary loss of calcium through the kidneys disrupts its reabsorption in the tubules and can also cause hypercalciuria (renal hypercalciuria). Idiopathic hypercalciuria can be hereditary.
The concentration of inorganic phosphorus in the serum is lowered by the absorption type III hypercalciuria due to the primary loss of phosphate through the kidneys. The concentration of PTH in renal hypercalciuria increases, because the primary disorder is a decrease in the reabsorption of calcium, which causes relative hypocalcemia and stimulates the release of PTH by the negative feedback principle. Absorptive hypercalciuria of type II calcium in daily urine is normal, as in patients on a diet with a calcium restriction (400 mg per day), because the absorption excess is not so significant. Nevertheless, the amount of calcium in the daily urine with a restriction of calcium intake for absorbent hypercalciuria I and III type, renal hypercalciuria remains high. Normal daily excretion of calcium in the urine with calcium restriction in food up to 400 mg per day is less than 200 mg / day. The concentration of calcium in the urine on an empty stomach is normally less than 0.11 mg / 100 ml of GFR. The normal ratio of calcium and creatinine in the urine is less than 0.2 after taking 1 g of calcium as a load.
The establishment of the type of idiopathic hypercalciuria is important for the selection of adequate drug therapy for nephrolithiasis.
Hypocalcauria - a decrease in the concentration of calcium in the urine - occurs with nephritis, severe hypoparathyroidism, hypovitaminosis D, hypothyroidism.
The study of calcium in urine is essential for the diagnosis of familial hypercalcemia-hypocalcauria, in which excretion of calcium with urine is less than 5 mmol / day in the presence of hypercalcemia.