Calcium - urine

Alternative names
Urinary Ca+2

Definition

This test measures the amount of calcium in urine. All cells require calcium for numerous functions. Calcium is especially important in the structure of bones and in neuromuscular activity.

A deficiency of calcium in the body fluids causes hyperexcitable nerves and muscles. Excess calcium has the opposite effect. Calcium is also an important component of kidney stones. Urinary calcium levels may therefore help identify causes of kidney stone formation.

How the test is performed
A 24-hour urine sample is generally needed:

     
  • On day 1, urinate into the toilet upon arising in the morning.  
  • Collect all subsequent urine (in a special container) for the next 24-hours.  
  • On day 2, urinate into the container in the morning upon arising.  
  • Cap the container. Keep it in the refrigerator or a cool place during the collection period. Label the container with your name, the date, the time of completion, and return it as instructed.

Your doctor will instruct you, if necessary, to stop taking any drugs that may interfere with the test.

For infants, thoroughly wash the area around the urethra. Open a Urine collection bag (a plastic bag with an adhesive paper on one end), and place it on your infant. For males, the entire penis can be placed in the bag and the adhesive attached to the skin. For females, the bag is placed over the labia. Place a diaper over the infant (bag and all). The infant should be checked frequently and the bag changed after the infant has urinated into the bag. For active infants, this procedure may take a couple of attempts - lively infants can displace the bag, causing an inability to obtain the specimen. The urine is drained into the container for transport to the laboratory.

Deliver it to the laboratory or your health care provider as soon as possible upon completion. The lab analyzes the sample for calcium content.

How to prepare for the test
No special preparation is necessary for this test, but if the collection is being taken from an infant, a couple of extra collection bags may be necessary.

How the test will feel
The test involves only normal urination, and there is no discomfort.

Why the test is performed
Calcium is usually measured to screen for or monitor diseases of the bone or calcium regulation disorders (that is, diseases of the parathyroid gland or kidneys). Urinary calcium levels aid the clinician in understanding how the kidneys handle calcium in certain disease states involving calcium balance including diseases of the parathyroid gland. Urinary calcium levels are also essential in the medical evaluation of kidney stones.

Normal Values

If a person is eating a normal diet, the expected amount of calcium in the urine is 100 to 300 mg/day. If eating a diet low in calcium, the amount of calcium in the urine will be 50 to 150mg/day.

Note: mg/day = milligrams per day

What abnormal results mean

Abnormal results are indicated as follows:

Increased or inappropriately high levels of urine calcium may indicate:

     
  • Idiopathic hypercalciuria  
  • Milk-alkali syndrome  
  • Hypoparathyroidism  
  • Renal tubular acidosis  
  • Sarcoidosis  
  • Vitamin D intoxication  
  • Renal failure  
  • Use of loop diuretics

Decreased levels of urine calcium may indicate:

     
  • Hyperparathyroidism  
  • Malabsorption (inadequate absorption of nutrients from the intestinal tract) disorders  
  • Vitamin D deficiency  
  • Use of thiazide diuretics

Additional conditions under which the test may be performed:

     
  • Secondary hyperparathyroidism

What the risks are
There are no risks.

Special considerations
There are some drugs that may interfere with this test. Drugs that may increase urine calcium measurements include: antacids, anticonvulsants, carbonic anhydrase inhibitor diuretics, and loop diuretics. Drugs that may decrease urine calcium measurements include: adrenocorticosteroids, oral contraceptives, and thiazide diuretics.

Johns Hopkins patient information

Last revised: December 6, 2012
by Dave R. Roger, M.D.

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