A urine test is a painless way for your doctor to check your
health and test for abnormalities. One thing your doctor 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 your kidneys aren’t
functioning properly, or that you aren’t drinking enough water.
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 doctor to tell if
your kidneys are trying to compensate for some abnormality.
Specific gravity testing is useful if your doctor thinks you
have any of the following conditions:
- dehydration or overhydration
- heart failure
- diabetes insipidus, a rare condition causing
thirst and the excretion of large amounts of diluted urine
- kidney failure
- kidney infection
- urinary tract infection
- hyponatremia, or low sodium levels
- hypernatremia, or elevated sodium
You may have to take a urine specific gravity test several
times in one day. This will help your doctor to see how well your kidneys are
Preparation for the test
Before you take a urine specific gravity test, your doctor
may ask you to do a few things to prepare for the test. 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 will likely need to wait to take the test if you’ve
recently been given intravenous contrast dye for an X-ray or MRI. 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 doctor 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, then
finish urinating into the toilet. This is known as the clean-catch or midstream
Your doctor 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 where a stick 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 doctor’s office
is that they can send the sample to the lab for more detailed testing and
Osmolality tests are sometimes used to evaluate how the
kidneys dilute and concentrate, with osmolality being the index of a
concentration. Knowing the osmolality of your urine can help your doctor
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 doctor 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:
Your doctor 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
- infection, such as a urinary tract
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
doctor 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 doctor 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 doctors with a differential diagnosis. When
used along with blood work or other urinalysis tests, it can also help doctors
identify different conditions.
In some cases, the urine specific gravity test will show
that you’re dehydrated or overhydrated. If you are extremely dehydrated and are
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 are overhydrated, your doctor may run more tests to look for
metabolic disorders, or liver, heart, or kidney conditions that could be