Urinalysis

A urinalysis is a group of chemical and microscopic tests. They detect the byproducts of normal and abnormal metabolism, cells, cellular fragments, and bacteria in urine. 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 excreted in the urine, traveling from the kidneys to the bladder and then through the urethra and out of the body. Urine is generally yellow and relatively clear, but each time someone urinates, the color, quantity, concentration, and content of the urine will be slightly different because of varying constituents.

Many disorders can be diagnosed in their early stages by detecting abnormalities in the urine. Abnormalities include increased concentrations of constituents that are not usually found in significant quantities in the urine, such as: glucose, protein, bilirubin, red blood cells, white blood cells, crystals, and bacteria. They may be present because:

1. there are elevated concentrations of the substance in the blood and the body is trying to decrease blood levels by “dumping” them in the urine,
2. kidney disease has made the kidneys less effective at filtering or,
3. of an infection, 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, clarity, and concentration;
2. chemical examination, which tests chemically for 9 substances that provide valuable information about health and disease; and
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 routine urinalysis usually consists of the visual and the chemical examinations. These two phases may be completed in the laboratory or doctor’s office. A microscopic examination is then performed if there is an abnormal finding on the visual or chemical examination, or if the doctor specifically orders it.

Urine for a urinalysis can be collected at any time. The first morning sample is considered the most valuable because it is more concentrated and more likely to yield abnormalities if present. It is important to clean the genitalia before collecting 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. As you 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. This type of collection is called a “midstream collection” or a “clean catch.”

A urine sample will only be useful for a urinalysis if taken to the doctor'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. However, at the time of sample collection, patients should follow instructions for a clean catch urine sample as stated above.