Calcium (Ca) in Urine

A test for calcium in urine is a 24-hour test that checks the amount of calcium that is passed from the body. Calcium is the most common mineral in the body and one of the most important. The body needs it to build and fix bones and teeth, help nerves work, make muscles squeeze together, help blood clot, and help the heart to work. Almost all of the calcium in the body is stored in bone. The rest is found in the blood.

Normally the level of calcium in the blood is carefully controlled. When blood calcium levels get low (hypocalcemia), the bones release calcium to bring it back to a good blood level. When blood calcium levels get high (hypercalcemia), the extra calcium is stored in the bones or passed out of the body in urine and stool. The amount of calcium in the body depends on the amount of:

• Calcium you get in your food.
• Calcium and vitamin D your intestines absorb.
• Phosphate in the body.
• Certain hormones, including parathyroid hormone, calcitonin, and estrogen in the body.

High calcium levels in the urine can cause kidney stones.

Vitamin D and these hormones help control the amount of calcium in the body. They also control the amount of calcium you absorb from food and the amount passed from the body in urine. The blood levels of phosphate are closely linked to calcium levels and they work in opposite ways: As blood calcium levels get high, phosphate levels get low, and the opposite is also true.

It is important to get the right amount of calcium [at least 1000 mg (1 g) a day] in your food because the body loses calcium every day. Foods rich in calcium are dairy products (milk, cheese), eggs, fish, green vegetables, and fruit. Most people who have low or high levels of calcium do not have any symptoms. Calcium levels need to be very high or low to cause symptoms.

A urine calcium test is done to:

• See whether a kidney stone has developed because of high amounts of calcium in the urine.
• Check for problems with the parathyroid glands.

A urine calcium test is not as helpful as a blood calcium test to find certain conditions, such as bone diseases or pancreatitis.

You may be asked to follow a special diet that is either high or low in calcium for several days before the test.

Urine calcium is measured in a sample taken from all the urine made in a 24-hour period.

Urine test

• You start collecting your urine in the morning. When you first get up, empty your bladder but do not save this urine. Write down the time that you urinated to mark the beginning of your 24-hour collection period.
• For the next 24 hours, collect all your urine. Your doctor or lab will usually provide you with a large container that holds about 1 gal (4 L). The container has a small amount of preservative in it. Urinate into a small, clean container and then pour the urine into the large container. Do not touch the inside of the container with your fingers.
• Keep the large container in the refrigerator for the 24 hours.
• Empty your bladder for the final time at or just before the end of the 24-hour period. Add this urine to the large container and record the time.
• Do not get toilet paper, pubic hair, stool (feces), menstrual blood, or other foreign matter in the urine sample.

There is no pain while collecting a 24-hour urine sample.

There is no chance for problems while collecting a 24-hour urine sample.

A test for calcium in urine is a 24-hour test that checks the amount of calcium that is passed from the body.

Normal

Normal results may vary from lab to lab.

Test results may be affected by the amount of calcium in the diet.

High values

• High levels of calcium in the urine may mean severe hyperthyroidism (thyrotoxicosis), hyperparathyroidism, cancers that have spread to the bones, Paget's disease, osteoporosis, sarcoidosis, or kidney disease. In some cases, calcium in the urine may be high for unknown reasons; this is called idiopathic hypercalciuria.
• High levels of urine calcium may also be caused by too much vitamin D or calcium in the diet from too much dairy products or calcium antacids.
• Dehydration can cause high levels of urine calcium.

Low values

• Low urine calcium levels may mean problems with the parathyroid glands (hypoparathyroidism), low amounts of calcium or vitamin D in the diet, poor absorption of calcium or vitamin D by the intestines, or kidney disease.
• Pregnant women and older men may also have low urine calcium levels.

Reasons you may not be able to have the test or why the results may not be helpful include:

• Too much or too little calcium in the diet.
• Taking medicines, such as diuretics, growth hormones, parathyroid hormone (PTH), antacids, or steroids.
• Taking too much vitamin D, lithium, laxatives, theophylline, or aspirin.
• Not collecting 24 hours of urine.
• Too much sun exposure, which affects vitamin D levels.
• Being on bed rest for a long time.

• Other tests that may be done to find the cause of abnormal urine calcium levels include blood tests for parathyroid hormone, chloride, alkaline phosphatase, and vitamin D. For more information, see the medical tests Parathyroid Hormone, Chloride (Cl), and Alkaline Phosphatase.
• Calcium levels can also be checked in a blood test. For more information, see the medical test Calcium (Ca) in Blood.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.