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.

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 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.

High calcium levels in the urine can cause kidney stones.

Why It Is Done

A urine calcium test is done to:

• See whether a kidney stone has developed because of high amounts of calcium in the urine.
• See how much calcium you are getting in your diet and how well it's being absorbed by your intestines.
• Look for problems that cause your bones to lose calcium.
• See how well your kidneys are working.
• 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 hyperparathyroidism, bone diseases, or pancreatitis.

How To Prepare

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