A urine concentration test determines how well your kidneys are functioning. The test may be used to test your kidneys’ response to:
- too much fluid intake (water loading)
- too little fluid intake (dehydration)
- a hormone that should (when being produced in the right amounts) concentrate your urine, antidiuretic hormone (ADH)
You may receive the test several times under different circumstances.
The test itself is painless. All you have to do is provide a clean-catch urine sample. However, the preparation phase may make you uncomfortable.
Your doctor may recommend urine concentration testing if you are urinating too much or too little. It can help identify specific types of problems with your kidneys.
The main reason this test is ordered is to see if you are suffering from central diabetes insipidus—a disease that causes excessive urination. This form of diabetes can occur when a head injury affects how your brain releases antidiuretic hormone (ADH). ADH normally increases the amount of water the kidneys retain. In central diabetes insipidus, your brain does not release enough ADH.
A urine concentration test can also be used to evaluate:
- kidney failure
- heart failure
- other hormone problems
- complications of a urinary tract infection
The test is based on a lab analysis of your urine.
Preparing For the Test
Depending on how the lab plans to analyze your urine, prior to the test you may be asked to:
- drink excess fluids
- avoid fluids for a period of time
- take ADH (which can be taken in either pill form or a nasal spray).
Taking a Clean-Catch Urine Sample
The urine concentration test requires a clean-catch urine sample. The goal of a clean catch is to avoid contaminating the urine sample with bacteria from your skin. You will be given a moist towelette and a specimen cup for the collection.
Wash your hands thoroughly with soap and warm water. Open the collection cup. Place the lid on a clean surface. Be careful not to touch the inside of the cup or the inside of the lid.
Use the moist towelette to clean the area around your urethra. Then begin to urinate into the toilet. After a few seconds, put the cup in your urine stream. Once you have collected enough urine, remove the cup. Finish urinating into the toilet. Then carefully recap the cup, being careful not to touch the inside of the container or lid.
Return the cup as instructed by your doctor. Your urine will be sent to a lab for testing.
The laboratory will test how concentrated your urine is. More concentrated urine means that there are more solutes and less water in the sample. Solutes are dissolved particles, such as sugars, salts and proteins.
Normal values may vary based on the laboratory used. However, according to the National Institutes of Health, typically, your urine is measured in specific gravity—the ratio of the density of your urine to the density of water. In this case, normal values are:
- 1.000 to 1.030 (this is the normal range)
- 1.001 after being given excessive amounts of water
- above 1.030 after refraining from drinking fluids
- concentrated after being given ADH (NIH, 2011)
If your urine is very concentrated, your doctor may suspect one or more of the following conditions:
- excess sweating
- glycosuria (too much sugar in your urine)
- heart failure
- narrowing of the renal arteries
- inappropriate ADH secretion
- excess vomiting
- fluid restriction
Low urine concentration suggests:
- too much fluid intake
- diabetes insipidus
- kidney failure
Combining multiple test preparations can help your doctor determine if your diabetes insipidus is due to a head injury and a resulting lack of ADH production, or because your kidneys cannot properly respond to ADH (called nephrogenic diabetes insipidus).
This test is not associated with any adverse side effects. However, refraining from drinking fluids for the test may make you feel dehydrated. Once the test is completed, ask your physician if you can resume drinking fluids. This will rehydrate your body.