Hypercalciuria is a condition marked by excessive calcium in the urine. While not serious in of itself, it can be a sign of deeper problems in the kidneys and/or bones, and a risk factor for developing these problems later in life. It is not preventable, but depending on its cause, it can be managed through diet, surgery, and/or drugs.
Definition & Facts
Normally, a person urinates between 100 and 300 milligrams (mg) of calcium per day. Calcium from the food you eat is normally absorbed by the intestines and passes into the blood, where the four parathyroid glands monitor calcium levels. If calcium levels rise, the parathyroids direct the kidneys and bones to reabsorb calcium to bring it down again. Any breakdown in this system can lead to excess calcium being excreted.
The condition is divided into three basic types: absorptive hypercalciuria, in which the intestines absorb too much calcium and pass it into the kidneys; renal leak hypercalciuria, in which the kidneys fail to reabsorb calcium properly and let it collect in the urine; and resorptive hypercalciuria, in which the parathyroids become uncontrolled and calcium intended for building bones is drawn off into the urine instead.
Symptoms & Complaints
It can cause calcium crystals to grow in the urinary tract and/or kidneys, which can develop into full-blown stones over time. While these crystals are too small to be noticeable in adults, in children they can sometimes cause painful urination and difficulty in urinating, back pain, and urinary tract infections.
Absorptive and renal leak hypercalciuria are most likely to form stones. Resorptive hypercalciuria does not increase the risk for kidney stones, but it does increase the risk for osteoporosis and other bone diseases.
Hypercalciuria is most often a hereditary condition. The patient's metabolism may be too efficient at absorbing calcium in the case of absorptive hypercalciuria, or the kidneys may be inefficient at absorbing calcium in the case of renal leak hypercalciuria. It can sometimes be caused by a diet that is too high in vitamin D and/or calcium, or too high in oxalates (an acid that interferes with the absorption of calcium). However, hypercalciuria that is caused solely by nutritional problems is rare.
Resorptive hypercalciuria is usually caused by an overactive parathyroid gland (hyperparathyroidism). The parathyroids normally direct calcium absorption in the kidneys and bone growth. Sometimes, however, one of the parathyroids develops a benign tumor known as an adenoma and begins to overproduce parathyroid hormone (PTH). The excessive PTH slows the deposition of calcium in the bones. Excess calcium is left in the bloodstream (hypercalcaemia) and eventually passes into the urine, while the bones, not receiving the calcium they need, become weaker.
Diagnosis & Tests
Hypercalciuria is diagnosed by a 24-hour urine test. Once the presence of high calcium urine is confirmed, the doctor may ask for a calcium load test, in which the patient eats a diet restricted in calcium and low in sodium for a week, and then is given a higher dose of calcium. If the patient's urine is still high in calcium after the restricted diet, the patient likely has renal leak hypercalciuria. The high dose of calcium at the end allows the doctor to test for absorptive hypercalciuria.
In order to determine the cause of the condition, the doctor will probably also call for a blood test for calcium levels and PTH levels, as well as examine any kidney stones that the patient has recently passed or had removed. If the patient has a low blood calcium level or a normal blood calcium level, that suggests absorptive or renal leak hypercalciuria, but if blood calcium and PTH levels are high as well, it is probably the resorptive type.
It is very important to distinguish the type, because treatments for absorptive and renal leak hypercalciuria will be ineffective for resorptive hypercalciuria and may even make the problem worse.
Treatment & Therapy
The first course of hypercalciuria treatment for absorptive or renal leak hypercalciuria is usually a change of diet. In particular, patients with this condition should be careful how much sodium and oxalate they get in their diet. They should also reduce their intake of meat and alcohol, increase the fiber and potassium in their diet, and increase their fluid intake (preferably water) to the point where they are producing about 2 liters of urine daily.
If changing the diet is not enough, the doctor may recommend a class of drugs called thiazides, which are diuretics that also stimulate the body's ability to absorb calcium and stabilize its level of parathyroid hormone. These are especially effective for absorptive or renal-leak hypercalciuria. Another possible drug treatment uses phosphate drugs, which stimulate the addition of calcium to the bones and remove it from the system. These will probably be used if the patient has osteoporosis and/or low bone minerals.
Finally, citrate supplements can help lower the risk of kidney stone formation. Patients who take calcium supplements, such as postmenopausal women with a risk of osteoporosis, may be switched to calcium citrate instead.
For resorptive hypercalciuria that is the result of an overactive parathyroid, surgery to remove part of the parathyroid is the best treatment. Parathyroid surgery is relatively simple and efficacious.
Prevention & Prophylaxis