Urine specific gravity

Alternative names:

urine density; urine s.g.

How the test is performed:

Child or adult:
Collect a "clean-catch" ("midstream") urine sample. To obtain a clean-catch sample, men or boys should wipe 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 (this clears the urethra of contaminants). Then, in a clean container, catch about 1 to 2 ounces of urine and remove the container from the urine stream. Give the container to the health care provider or assistant.

Infant:
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). Check your baby frequently and remove the bag after the infant has urinated into it. 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 a container for transport back to the health care provider.

How to prepare for the test:

The health care provider may advise you to withhold drugs that can affect the test (see "special considerations").

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

Submit a urine sample to the laboratory.
If the specimen may be contaminated by vaginal discharge or bleeding, then collect a clean-catch sample, - See urine culture (clean catch).

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:

Specific gravity measures the concentration of particles in a solution (i.e., grams/ml). Osmolality is a more exact measurement of urine concentration than specific gravity because specific gravity depends on the precise nature of the molecules present in the urine. Specific gravity also requires correction for the presence of glucose or protein. But the specific gravity measurement is easier and more convenient to test and frequently makes the osmolality measurement unnecessary.