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urine osmolality test

Alternative Names 
urine osmolality

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.
  • congestive heart failure, or a weakened heart that fails to pump enough blood to body cells
Abnormally low osmolality may be a sign of:
  • aldosteronism, a condition in which a person has too much of the hormone aldosterone, which helps the body break down and use sodium, chloride, and potassium
  • diabetes insipidus, a disease which causes increased thirst and urination
  • excessive fluid intake, which occurs when a person drinks too much fluid
  • kidney damage or disease
  • pyelonephritis, a kidney inflammation usually caused by an infection
Author: David T. Moran, MD
Reviewer: eknowhow Medical Review Panel
Editor: Dr John Hearnr
Last Updated: 26/05/2005
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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