Urinalysis

A urinalysis is a group of physical, chemical, and microscopic tests. The tests detect and/or measure several substances in the urine, such as byproducts of normal and abnormal metabolism, cells, cellular fragments, and bacteria.

Urine is produced by the kidneys, two fist-sized organs located on either side of the spine at the bottom of the ribcage. The kidneys filter wastes out of the blood, help regulate the amount of water in the body, and conserve proteins, electrolytes, and other compounds that the body can reuse. Anything that is not needed is eliminated in the urine, traveling from the kidneys through ureters to the bladder and then through the urethra and out of the body. Urine is generally yellow and relatively clear, but each time a person urinates, the color, quantity, concentration, and content of the urine will be slightly different because of varying constituents.

Many disorders may be detected in their early stages by identifying substances that are not normally present in the urine and/or by measuring abnormal levels of certain substances. Some examples include glucose, protein, bilirubin, red blood cells, white blood cells, crystals, and bacteria. They may be present because:

1. There is an elevated level of the substance in the blood and the body responds by trying to eliminate the excess in the urine.
2. Kidney disease is present.
3. There is a urinary tract infection present, as in the case of bacteria and white blood cells.

A complete urinalysis consists of three distinct testing phases:

1. Visual examination, which evaluates the urine's color and clarity
2. Chemical examination, which tests chemically for about 9 substances that provide valuable information about health and disease and determines the concentration of the urine
3. Microscopic examination, which identifies and counts the type of cells, casts, crystals, and other components such as bacteria and mucus that can be present in urine

A microscopic examination is typically performed when there is an abnormal finding on the visual or chemical examination, or if a healthcare practitioner specifically orders it.

Abnormal findings on a urinalysis may prompt repeat testing to see if the results are still abnormal and/or may be followed by additional urine and blood tests to help establish a diagnosis.

One to two ounces of urine is collected in a clean container. A sufficient sample is required for accurate results.

Urine for a urinalysis can be collected at any time. In some cases, a first morning sample may be requested because it is more concentrated and more likely to detect abnormalities.

Sometimes, you may be asked to collect a "clean-catch" urine sample. For this, it is important to clean the genital area before collecting the urine. Bacteria and cells from the surrounding skin can contaminate the sample and interfere with the interpretation of test results. With women, menstrual blood and vaginal secretions can also be a source of contamination. Women should spread the labia of the vagina and clean from front to back; men should wipe the tip of the penis. Start to urinate, let some urine fall into the toilet, then collect one to two ounces of urine in the container provided, then void the rest into the toilet.

A urine sample will only be useful for a urinalysis if taken to the healthcare provider's office or laboratory for processing within a short period of time. If it will be longer than an hour between collection and transport time, then the urine should be refrigerated or a preservative may be added.

No advance test preparation is needed.