What is Specific Gravity?
A urine test is a painless way for your healthcare provider to check your health and test for abnormalities. One thing your healthcare provider may check for in your urine sample test, or urinalysis, is specific gravity.
A urine-specific gravity test compares the density of urine to the density of water. This quick test can help determine how well your kidneys are diluting your urine.
Urine that’s too concentrated could mean that your kidneys aren’t functioning properly or that you aren’t drinking enough water.
Urine that isn’t concentrated enough can mean you have a rare condition called diabetes insipidus, which causes thirst and the excretion of large amounts of diluted urine.
What is the test used for?
The main role of your kidneys is to filter your blood and maintain a normal electrolyte balance. Testing urine-specific gravity is a quick way for your healthcare provider to tell if your kidneys are trying to compensate for some abnormality.
Specific gravity testing is useful if your healthcare provider thinks you have any of the following conditions:
- dehydration or overhydration
- heart failure
- diabetes insipidus
- kidney failure
- kidney infection
- urinary tract infection
- hyponatremia, or low sodium levels
- hypernatremia, or elevated sodium levels
You may have to take a urine-specific gravity test several times in one day. This will help your healthcare provider to see how well your kidneys are compensating.
What preparation is required?
Before you take a urine-specific gravity test, your healthcare provider may ask you to do a few things to prepare for it. First, they’ll ask you to stop taking any medications that could interfere with the test results, such as those containing sucrose or dextran.
You’ll likely need to wait to take the test if you’ve recently been given intravenous contrast dye for an X-ray or MRI scan. If it’s been more than three days since the dye was administered, it should be fine for you to take the urine test.
You should also eat a balanced diet in the days leading up to the test. This diet should exclude certain foods that can affect the color of your urine. These include:
- fava beans
How is the test performed?
A sample for a urine-specific gravity test contains at least 1 to 2 ounces of urine. The best time to get a sample is first thing in the morning when your urine is the most concentrated.
Your healthcare provider will give you a cup to collect a urine sample.
For the best sample, you should use an antibacterial wipe to clean the area around your urethra. This will reduce the likelihood that bacteria will contaminate the sample.
Urinate a small amount, and then place the cup under your urine stream. Urinate into the cup until you have a large enough sample, and then finish urinating into the toilet. This is known as the clean-catch (or midstream) method.
Your healthcare provider will send the urine sample to a laboratory while it’s fresh. This will ensure the best results.
A lab technician will use a refractometer to project light into the sample and determine its density. This is more reliable than the dipstick method, in which a stick is placed in the urine to measure how much it sinks or floats.
While there are home tests, the results won’t be as accurate as those conducted by a professional in a sterile environment. Home tests are more susceptible to contamination.
Another benefit to taking the test at your healthcare provider’s office is that they can send the sample to the lab for more detailed testing and analysis.
Osmolality tests are sometimes used to evaluate how the kidneys dilute and concentrate urine, with osmolality being the index of a concentration. Knowing the osmolality of your urine can help your healthcare provider diagnose certain conditions.