A test for calcium in urine is a 24-hour test that checks the amount of calcium that is passed from the body in the urine. 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.
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.
How It Is Done
Urine calcium is measured in a sample taken from all the urine made in a 24-hour period.
- 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.
How It Feels
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.
The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Test results may be affected by the amount of calcium in the diet.
|Low amount of calcium in diet:|
|Average amount of calcium in diet:||
100-250 mg per day or 2.5-6.2 mmol per day
|High amount of calcium in diet:||
250-300 mg per day or 6.2-7.5 mmol per day
High values of calcium in the urine may be caused by:
In some cases, calcium in the urine may be high for other reasons. One example of this is idiopathic familial hypocalciuric hypercalcemia.
Low values of calcium in the urine may be caused by:
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Eating or drinking too much or too little calcium before the test. For the best results, follow the instructions on how much calcium to have before the test.
- Taking medicines, such as diuretics. Many medicines can affect calcium levels in the blood.
- Not collecting 24 hours' worth of urine.
- Being on bed rest for a long time.
What To Think About
- 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.
- Calcium levels can also be checked in a blood test. To learn more, see the topic Calcium (Ca) in Blood.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerChristopher G. Wood, MD, FACS - Urology, Oncology
Current as ofAugust 21, 2015