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Urine Osmolality Test


Overview & Description

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 healthcare provider or lab for testing.


    Preparation & Expectations

    What is involved in preparation for the test?

    Since test preparations vary, a person should ask a healthcare provider for specific instructions.


    Results and Values

    What do the test results mean?

    Normally, urine has an osmolality of 50 to 1,400 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 adenal 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

  • Attribution

    Author:David T. Moran, MD
    Date Written:
    Editor:Coltrera, Francesca, BA
    Edit Date:05/31/00
    Reviewer:Eileen McLaughlin, RN, BSN
    Date Reviewed:09/20/01

    Sources

    Tabers Cyclopedic Medical Dictionary, F.A.Davis, 1993

    Illustrated Guide to Diagnostic Tests, Springhouse, 1998

    Mosby's Manual of Diagnostic and laboratory Tests, Kathleen Pagana and Timothy Pagana, 1998


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