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The osmolality urine test measures the concentration of particles in urine.
Osmolality (particles per kilogram of water) and osmolarity (particles per liter of solution) are sometimes confused. But for dilute fluids such as urine, they are essentially the same.
Osmolality can also be measured using a blood test.
A clean-catch urine sample is needed. The clean-catch method is used to prevent germs from the penis or vagina from getting into a urine sample. To collect your urine, the health care provider may give you a special clean-catch kit that contains a cleansing solution and sterile wipes. Follow instructions exactly so that the results are accurate.
Your health care provider will ask you to temporarily stop any medicines that may affect the test results. Be sure to tell your provider about all the medicines you take, including dextran and sucrose. Do not stop taking any medicine before talking to your doctor.
Also tell your provider if you recently received intravenous dye (contrast medium) for an x-ray. The dye can also affect test results.
The test involves normal urination. There is no discomfort.
This test helps check 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:
Normal values vary from lab to lab. Talk to your doctor about the meaning of your specific test results.
Abnormal results are indicated as follows:
Greater-than-normal measurements may indicate:
Lower-than-normal measurements may indicate:
There are no risks with this test.
Gerber GS, Brendler CB. Evaluation of the urologic patient: history, physical examination, and urinalysis. In: Wein AJ, Kavoussi LR, Novick AC, et al., eds. Campbell-Walsh Urology. 10th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 3.
McPherson RA, Ben-Ezra J. Basic examination of urine. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 28.