The test requires a clean-catch urine sample. For information on how to collect this urine sample, see: Clean-catch urine culture
How to prepare for the test
Your health care provider will instruct you, if necessary, to discontinue 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 only normal urination, and there is no discomfort.
Why the test is performed
This test helps evaluate your body's water balance and urine concentration.
Normal values are between 1.000 to 1.030.
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.
Additional conditions under which the test may be performed:
Complicated UTI (pyelonephritis)
High blood sodium level (hypernatremia)
Low blood sodium level (hyponatremia)
Osmolality is a more specific test for urine concentration. However, the specific gravity measurement is easier and more convenient and usually part of a routine urinalysis. It frequently makes the osmolality measurement unnecessary.
Landry DW, Bazari H. Approach to the patient with renal disease. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 116.
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.