Definition A urine osmolality test measures the osmolality, or concentration of particles, in a person's urine. It provides information about the body's ability to balance fluids and other substances.
Who is a candidate for the test? A urine osmolality test is done when fluid balance or kidney problems are suspected.
How is the test performed? A mid-stream, or clean-catch, urine sample is required for this test. First, the entire area around the urethra should be washed off to prevent contamination of the sample. Then, a person should:
start urinating into the toilet
move the container to catch a sample of urine
take away the container and finish urinating into the toilet
The container should be covered and brought to the doctor or laboratory for testing.
What is involved in preparation for the test? Since test preparations vary, a person should ask a doctor for specific instructions.
What do the test results mean? Normally, urine has an osmolality of 50 to 1,200 mOsm/kg H20 (milliosmoles per kilogram of water).
Abnormally high osmolality may be a sign of:
Addison's disease, which is caused by a deficiency of hormones produced in the adrenal glands
irregularities in the secretion of antidiuretic hormone, or ADH. ADH helps the kidneys put water back into the bloodstream.
Author: David T. Moran, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearnr Last Updated: 26/05/2005 Contributors Potential conflict of interest information for reviewers available on request
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