|Back to article|
Osmolality - urine
The osmolality urine test the concentration of particles in urine. Osmolality (particles/kg water) and osmolarity (particles/liter of solution) are sometimes confused, but for dilute fluids such as urine they are essentially the same.
A blood test may also be done to measure osmolality. See: Serum osmolality
How the test is performed
A "clean-catch" (midstream) urine sample is needed. For information on how to collect the sample, see clean catch urine culture.
How to prepare for the test
Your health care provider will tell you if you need to stop taking any drugs that may interfere with the test. Drugs that can increase specific gravity measurements include dextran and sucrose.
Receiving intravenous dye (contrast medium) for an x-ray exam up to 3 days before the test can also interfere with results.
Eat a normal, balanced diet for several days before the test.
How the test will feel
The test involves normal urination, and there is no discomfort.
Why the test is performed
This test helps evaluate your body's water balance and urine concentration.
Osmolality is a more exact measurement of urine concentration than the urine specific gravity test.
Normal values are as follows:
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
Abnormal results are indicated as follows:
Greater-than-normal measurements may indicate:
Lower-than-normal measurements may indicate:
Additional conditions under which the test may be performed:
Bazari H. Approach to the patient with renal disease. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 115.
Reviewed by:David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is an independent audit to verify that A.D.A.M. follows rigorousstandards of quality and accountability. A.D.A.M. is among the first to achieve this important distinction for online health information andservices. Learn more about A.D.A.M.'s editorialpolicy, editorialprocess, and privacypolicy. A.D.A.M. is also a founding member of Hi-Ethics and subscribes to the principles of the Health on the Net Foundation (www.hon.ch.)
The information provided herein should not be used during any medical emergency or for the diagnosis or treatmentof any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions.Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 2014 A.D.A.M., Inc. Any duplication ordistribution of the information contained herein is strictly prohibited.