Urinalysis

What is the test?

A urinalysis is a routine examination of the urine for cells, tiny structures, bacteria, and chemicals that suggest various illnesses, including infection, diabetes, kidney problems and liver disease. A urine culture attempts to grow large numbers of bacteria from a urine sample to diagnose a bacterial urine infection.

How do I prepare for the test?

For a regular urinalysis, you are asked to urinate briefly into a plastic cup. When urine is collected for a urine culture, you must provide a "clean catch" sample - one that is not contaminated by skin cells and skin bacteria. This is so the doctor can obtain a sample of urine from inside your bladder, where normally there should be no bacteria. In contrast, there are many bacteria on the skin of a penis or in a vagina. The trick (harder for a woman than a man) is to pee directly into a sterile container without having the stream of urine first touch your skin or the nonsterile tissues of the vagina.

To collect a clean catch sample, you are given a sterile plastic container and asked to wipe off the area around your urethra (where urine exits) with an antiseptic cloth. For women, it's also helpful to hold the two labia (outer walls) of the vagina apart with one hand when you urinate, so that the stream of urine passes directly into the sterile container. Since the first flow of urine is most likely to be contaminated by bacteria from around the opening of the urethra, first urinate for a moment into the toilet and then use the cup to collect the "middle" portion of your urine stream.

What happens when the test is performed?

For a regular urinalysis, your urine is tested both chemically and by microscopic exam. Chemical examination uses a "dipstick" to reveal the pH (acidity) and concentration of your urine, while simultaneously testing for several chemicals at once. Some chemicals indicate that blood in general and white blood cells in particular might be present, a sign of a urinary infection, kidney stones, or other problems. Nitrite, a chemical produced by most bacteria, suggests a bacterial infection. Sugar in the urine is a sign of diabetes (high blood sugar), while chemicals known as ketones can indicate a diabetic complication. Protein in the urine can indicate kidney disease or impaired kidney function.

A microscopic examination is done after the urine is spun inside a tube in a centrifuge. This concentrates the solid particles at the bottom of the tube, so they can be studied more easily. Microscopic examination can show red blood cells, white blood cells, bacteria, crystals, skin cells that might have contaminated the sample, and, rarely, parasites in your urine. In some cases, the way the cells look offers your doctor clues about whether they entered your urine from the bladder or the kidney.

What risks are there from the test?

None.

Must I do anything special after the test is over?

No.

How long is it before the result of the test is known?

Your doctor might be able to do a urinalysis in his or her office and can give you the results within 10-15 minutes. If the urine is sent to a separate laboratory, it usually takes several hours to get results, so you may not hear from your doctor until the next day. A urine culture takes 24 to 72 hours to complete, so you may not hear results for several days.