The osmolality urine test measures the concentration of particles in urine.
Osmolality (particles per kilogram of water) and osmolarity (particles per liter of solution) are sometimes confused. But for dilute fluids such as urine, they are essentially the same.
Osmolality can also be measured using a
How the test is performed
How to prepare for the test
Your health care provider will ask you to temporarily stop any medicines that may affect the test results. Be sure to tell your provider about all the medicines you take, including dextran and sucrose. Do not stop taking any medicine before talking to your doctor.
Also tell your provider if you recently received intravenous dye (contrast medium) for an x-ray. The dye can also affect test results.
How the test will feel
The test involves normal urination. There is no discomfort.
Why the test is performed
This test helps check your body’s water balance and urine concentration.
Osmolality is a more exact measurement of urine concentration than the
Normal values are as follows:
- Random specimen: 50 to 1200 milliosmoles per kilogram (mOsm/kg)
- 12 to 14 hour fluid restriction: Greater than 850 mOsm/kg
Normal values vary from lab to lab. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
Abnormal results are indicated as follows:
Greater-than-normal measurements may indicate:
- Loss of body fluids (dehydration)
- Narrrowing of hte kidney artery (renal artery stenosis)
- Sugar, or glucose, in the urine
Syndrome of inappropriate ADH secrettion (
Lower-than-normal measurements may indicate:
- Damage to kidney tubule cells (
renal tubular necrosis)
- Drinking too much fluid
- Kidney failure
- Severe kidney infection (pyelonephritis)
What the risks are
There are no risks with this test.