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Urine specific gravity

Definition

Urine specific gravity is a laboratory test that measures the concentration of particles in the urine.

See also:

• Urine concentration test
• Urine osmolality
• Urinalysis

Alternative Names

Urine density

How the test is performed

The test requires a clean-catch urine sample.

To obtain a clean-catch sample, men or boys should clean the head of the penis.

Women or girls need to wash the area between the lips of the vagina with soapy water and rinse well.

As you start to urinate, allow a small amount to fall into the toilet bowl to clear the urethra of contaminants. Then, put a clean container under your urine stream and catch 1 to 2 ounces of urine. Remove the container from the urine stream. Cap and mark the container and give it to the health care provider or assistant.

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 the infant. For boys, the entire penis can be placed in the bag and the adhesive attached to the skin. For girls, the bag is placed over the labia. Diaper as usual over the secured bag. This procedure may take a couple of attempts -- lively infants can displace the bag. The infant should be checked frequently and the bag changed after the infant has urinated into the bag. The urine is drained into the container for transport to the laboratory.

How to prepare for the test

Your health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test. Drugs that can increase specific gravity measurements include dextran and sucrose. Receiving intravenous dye (contrast medium) for an x-ray exam up to 3 days before the test can also interfere with results.

Eat a normal, balanced diet for several days before the test.

How the test will feel

The test involves only normal urination, and there is no discomfort.

Why the test is performed

This test helps evaluate your body's water balance and urine concentration.

Normal Values

Normal values are between 1.002 to 1.028.

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

Increased urine specific gravity may be due to:

• Dehydration
• Diarrhea
• Excessive sweating
• Glucosuria
• Heart failure (related to decreased blood flow to the kidneys)
• Renal arterial stenosis
• Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
• Vomiting
• Water restriction

Decreased urine specific gravity may be due to:

• Excessive fluid intake
• Diabetes insipidus - central
• Diabetes insipidus - nephrogenic
• Renal failure (that is, loss of ability to reabsorb water)
• Pyelonephritis

Additional conditions under which the test may be performed:

• Acute tubular necrosis
• Complicated UTI (pyelonephritis)
• Hepatorenal syndrome
• Interstitial nephritis

What the risks are

There are no risks.

Special considerations

Osmolality is a more specific test for urine concentration. However, the specific gravity measurement is easier and more convenient. It frequently makes the osmolality measurement unnecessary.

Review Date:10/22/2007
Reviewed By:Robert Mushnick, M.D., Clinical Assistant Professor, Department of Nephrology, SUNY Downstate Health Center, Brooklyn, NY. Review provided by VeriMed Healthcare Network.

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