A urine concentration test measures the ability of the kidneys to conserve or excrete water appropriately.
Water loading test; Water deprivation test
For this test, the specific gravity of urine is measured before and after one or more of the following:
The test requires a clean-catch urine sample.
To obtain a clean-catch sample, men or boys should clean the head of the penis. Women or girls need to wash the area between the lips of the vagina with soapy water and rinse well.
As you start to urinate, allow a small amount to fall into the toilet bowl to clear the urethra of contaminants. Then, put a clean container under your urine stream and catch 1 to 2 ounces of urine. Remove the container from the urine stream. Cap and mark the container and give it to the health care provider or assistant.
For infants, thoroughly wash the area around the urethra. Open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on the infant. For boys, the entire penis can be placed in the bag and the adhesive attached to the skin. For girls, the bag is placed over the labia. Diaper as usual over the secured bag.
This procedure may take a couple of attempts -- lively infants can displace the bag. The infant should be checked frequently and the bag changed after the infant has urinated into the bag. The urine is drained into the container for transport to the laboratory.
Eat a normal, balanced diet for several days before the test. Your health care provider will give you instructions for water loading or water deprivation.
Your health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test. Drugs that can affect measurements include dextran and sucrose, and x-ray contrast medium (dye) received within 3 days.
The test involves only normal urination, and there is no discomfort.
This test may also be done if you have signs of SIADH (syndrome of inappropriate ADH).
In general, 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.
Increased urine concentration may indicate:
Decreased urine concentration may indicate:
Additional conditions under which the test may be performed:
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.
Shorecki K, Ausiello D. Disorders of sodium and water homeostasis. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 118.