Water loading test; Water deprivation test
A urine concentration test measures the ability of the kidneys to conserve or excrete water.
After you provide a urine sample, it is tested right away. For urine specific gravity, the health care provider uses a dipstick made with a color-sensitive pad. The dipstick color changes and tells the provider the specific gravity of your urine. The dipstick test gives only a rough result. For a more accurate specific gravity result or measurement of urine electrolytes or osmolality, your provider will send your urine sample to a lab.
If needed, your provider will ask you to collect your urine at home over 24 hours. Your provider will tell you how to do this. Follow instructions exactly.
Eat a normal, balanced diet for several days before the test. Your provider will give you instructions for water loading or water deprivation.
Your 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 provider.
Also tell your provider if you recently received intravenous dye (contrast medium) for an imaging test such as a CT or MRI scan. The dye can also affect test results.
The test involves only normal urination. There is no discomfort.
This test may also be done if you have signs of syndrome of inappropriate ADH (SIADH).
In general, normal values for specific gravity are as follows:
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
Increased urine concentration may be due to different conditions, such as:
Decreased urine concentration may indicate:
There are no risks with this test.
Fogazzi GB, Garigali G. Urinalysis. In: Feehally J, Floege J, Tonelli M, Johnson RJ, eds. Comprehensive Clinical Nephrology. 6th ed. Philadelphia, PA: Elsevier; 2019:chap 4.
Riley RS, McPherson RA. Basic examination of urine. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. St Louis, MO: Elsevier; 2017:chap 28.BACK TO TOP
Review Date: 7/7/2019
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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