What is Urine Specific Gravity?

Urine specific gravity is a measurement of the volume of particles in the urine. It is performed as part of a routine urinalysis, an examination of a urine sample. Urinalysis is an important diagnostic tool that allows lab technicians to run a number of tests on a urine sample to provide information about a patient's health. In cases where suspected kidney or bladder disease are involved, the urinalysis can be used to narrow down possible diagnoses so that a treatment plan can be developed.

Urine is a blend of fluids and concentrated molecules expressed by the kidneys. These molecules are waste materials that the body cannot use. When the concentration of particles in the urine is high, it can be an indicator that a patient is dehydrated or experiencing another medical problem like heart failure. When the concentration is unusually low, it means that the patient may be consuming too many fluids, and may have a condition such as diabetes.

In the urine specific gravity test, the patient is asked for a clean catch sample. The patient washes or wipes the genitals before urinating to clear any contaminants in the urethra and then urinates into a sample cup. The contents of the cup are analyzed in the lab. Many clinics have the ability to run basic tests in house and can return results very quickly. Such samples are often collected at the start of a medical visit so that the urinalysis can be done while the patient is being examined, providing results by the end of the appointment.

Determining urine specific gravity can be done very quickly, efficiently, and cheaply. Low-cost and low-technology evaluation and assessment tools are important in many clinical settings. Using a low cost test can eliminate the need for a more expensive test or procedure. This saves money for the patient and also reduces the need for invasive medical tests that might put the patient at risk.

There are some things that can skew urinalysis results and cause problems with the test. Some medications can interfere with the ability to concentrate the urine, making the urine more or less concentrated than unusual. Patients who have undergone medical imaging studies with contrast media will also have unusually high urine specific gravity because their kidneys are working overtime to express the contrast medium. Surgery can be another factor that may interfere with the reliability of the test. Patients should alert their doctors to any recent events in their medical history before the urine specific gravity test is performed.