Urine Specific Gravity Test
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 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 of 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.
How are the results interpreted?
To understand urine concentrations, think about the dark color of your urine when you haven’t had anything to drink in some time. Your urine is lighter and usually has lower specific gravity when you’re well-hydrated.
Urine specific gravity is a more precise measurement of your urine’s overall concentration than looking at the color of your urine alone.
Your healthcare provider will look at the ratio of the density of your urine to the density of water. To put it another way, the specific density of water would be 1.000. Ideally, urine specific gravity results will fall between 1.002 and 1.030 if your kidneys are functioning normally.
Specific gravity results above 1.010 can indicate mild dehydration. The higher the number, the more dehydrated you may be.
High urine specific gravity can indicate that you have extra substances in your urine, such as:
- red blood cells
- white blood cells
Your healthcare provider will use the results from your urine specific gravity test, along with other urinalysis results, to come up with a diagnosis. Abnormal specific gravity results could indicate:
- excess substances in the blood
- kidney disease (high or low specific gravity can indicate an inability of the kidney tubules to function correctly)
- infection, such as a urinary tract infection
- brain injuries, which can cause a person to develop diabetes insipidus
A urinalysis can also measure the concentration of various cells. White blood cells can indicate an infection. And glucose can point to glucose intolerance or diabetes.
Other types of urine tests include urine pH tests, hemoglobin tests, and ketone tests. The results from these tests can help your healthcare provider make a more accurate diagnosis.
What are the test’s side effects?
The urine specific gravity test involves urinating normally and isn’t associated with any harmful side effects. However, if you have a urinary tract infection, urinating may cause a burning or painful sensation.
Always notify your healthcare provider if you experience discomfort urinating or any unexpected symptoms.
A urine specific gravity test is a painless and easy test to take. Preparation is simple, and it only requires excluding a few things from your diet and temporarily stopping certain medications.
This test can help healthcare providers with a differential diagnosis. When used along with blood work or other urinalysis tests, it can also help healthcare providers identify different conditions.
In some cases, the urine specific gravity test will show that you’re dehydrated or overhydrated. If you’re extremely dehydrated and having trouble getting enough fluids, you may be given intravenous fluids to help hydrate you faster.
Mild dehydration can be resolved by consistently drinking more water. If you’re overhydrated, your healthcare provider may run more tests to look for metabolic disorders or liver, heart, brain, or kidney conditions that could be causing it.