Examination of the urine for the purpose of diagnosing or monitoring a medical condition. Urinalysis can help uncover conditions such as gout, kidney disease, diabetes, and urinary tract infection. It is also used to help detect lupus nephritis, a common complication of systemic lupus erythematosus (SLE). In general, urinalysis by itself does not provide enough information for a doctor to make a diagnosis. However, it is often used to assist a diagnosis or suggest other tests that may be needed.
There are three basic components of urinalysis: a physical analysis, a microscopic analysis, and a chemical analysis of urine. For the physical analysis, a health professional looks at the urine and notes its physical characteristics, including its color and whether it is clear or cloudy. (Several conditions can cause cloudy urine, including kidney disease and infections of the kidney, bladder, and urinary tract—although cloudy urine may also be due to something as harmless as a big meal.) A test called the urine specific gravity test, which determines the concentration of particles in the urine, can also point to dehydration or kidney problems.
For a microscopic analysis, a sample of urine is put under a microscope and examined for blood, bacteria, crystals, and other substances. Red blood cells in the urine may be harmless and can be due to exercise or medicines such as aspirin, but they may also be the result of a serious condition such as a kidney disorder or tumor. White blood cells in the urine often point to urinary tract infections, and bacteria in the urine also suggest infection. Uric acid crystals in the urine may be a sign of gout.
A chemical analysis uses a dipstick — a multicolored chemical-coated strip that, when dipped in urine, changes its colors in the presence of various substances — to test for many different substances in the urine. A positive test for glucose in the urine can point toward diabetes. (Many medicines can also cause glucose in the urine.) Tests for a protein called albumin in the urine are common and can help diagnose kidney disease, a common complication of diabetes and, as discussed below, SLE. Ketones in the urine may indicate diabetes or an eating disorder, bilirubin may point to liver disease, and nitrates may be a sign of a urinary tract infection.
Before a doctor prescribes a drug, urinalysis is often recommended to test for conditions that may make the drug unsafe to take. In some cases, urinalysis is part of the regular workup to make sure a drug is not causing unintended side effects. For example, because corticosteroid drugs can raise the risk for Type 2 diabetes, people taking corticosteroids are advised to have their urine examined periodically for glucose.
In people with SLE, urinalysis is used to test for lupus nephritis, a kidney disorder that is one of SLE’s most common complications. Tests for lupus nephritis include a dipstick test for protein in the urine and a microscopic analysis for blood. The urine of people with lupus nephritis may have a foamy appearance. A biopsy of the kidney may also be done to confirm the diagnosis.