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Urine concentration test
Alternative namesWater loading test; Water deprivation test
DefinitionA urine concentration test measures the ability of the kidneys to conserve or excrete water appropriately. (See also urine specific gravity .)
How the test is performed
Collect a "clean-catch" (midstream) 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.
Water loading means you drink excessive amounts of water or you receive intravenous solutions. Water deprivation means you do not drink fluids for a period of time.
How to prepare for the testEat a normal, balanced diet for several days before the test. Submit a urine sample to the laboratory. If contamination of the specimen (by vaginal discharge or bleeding) is likely, collect a clean-catch sample.
Instructions will be given for water loading or water deprivation. The health care provider may advise you to withhold drugs that can affect the test.
If the collection is being taken from an infant, a couple of extra collection bags may be necessary.
How the test will feelThe test involves only normal urination, and there is no discomfort.
Why the test is performed
Most often, a urine concentration test is performed when diabetes insipidus is suspected and to help differentiate it from nephrogenic diabetes insipidus .
SIADH (syndrome of inappropriate ADH ) -- a condition where urine concentrations are excessively high (water is conserved) given the state of an individual's degree of hydration -- is another condition where urine concentration values are helpful for diagnostic and therapeutic purposes.
Normal values are indicated as follows (normal value ranges may vary slightly among different laboratories):
What abnormal results mean
Increased urine specific gravity may indicate:
Special considerationsDrugs that can increase specific gravity measurements include dextran and sucrose, and radiographic contrast medium within 3 days.
Update Date: 2/11/2004Irfan A. Agha, M.D., Department of Medicine, Renal Division, St. Louis University, St. Louis, MO. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT