Why Are Patients Asked for Urine Samples?

August 12, 2014, 10:06am EDT

Have you ever wondered why health professionals ask for a urine sample? The kidneys remove waste material, fluids, and other substances from the blood. The urine can contain many different clues to how your body is doing. Your urine tells a lot about your health. Testing the urine is known as “urinalysis” (analysis of the urine). The most common use of urinalysis is to detect substances or cells in the urine that point to different disorders.

Urinalysis is used to diagnose disease or to screen for health problems. In some cases, kidney disease might be suspected based on what is found. In other cases, nothing important is found. The results of urine tests can be affected by diet, dehydration, medicines, exercise, and other factors. Sometimes, you will be asked to come back and give another sample.

Many people are familiar with pregnancy tests that use urine to detect a substance that only pregnant women produce. Others are familiar with tests of the urine for employment or to test athletes, for example, to exclude drug use. But there are many other uses in medicine.

To check your general health, everyone should have a urinalysis as a child and then periodically as an adult. Some doctors use urinalysis as part of a routine medical exam to screen for early signs of disease, including chronic kidney disease. If you already know you have diabetes, or chronic kidney disease, a urinalysis will be used to monitor you. If a urinary tract infection is suspected, a urine test may show blood or bacteria in the urine.

What exactly could they find in urine? Often, substances such as protein or glucose (sugar) will begin to appear in the urine before patients are aware that they may have a problem. Persistent protein in the urine (two positive tests for protein over several weeks) is one of the earliest signs of chronic kidney disease. A large amount of glucose in the urine is a sign of potential diabetes. Urine tests can be used to diagnose urinary tract infections, if bacteria or white blood cells are found.

In patients who have already been diagnosed with chronic kidney disease, urinalysis may be ordered at intervals as a quick and useful way to monitor function. It can also provide information about whether treatment is reducing the amount of protein in the urine.

A urinalysis has three parts:

  1. Visual examination of the urine sample for color and clearness. Blood may make urine look red or the color of tea or cola. An infection may make urine look cloudy.
  2. A dipstick examination, which uses a chemically treated strip. Strips can check for many things in addition to protein and glucose including: pregnancy, because a hormone that is only made by pregnant women can be found; certain legal and illegal drugs that are processed by the kidney; pH is a measure of the amount of acid in the urine. An abnormal pH may be a sign of kidney stones, urinary infections, chronic kidney disease or certain disorders that affect growth and development in children; creatinine gives an estimate of the concentration of your urine, which allows for a more accurate protein result. Creatinine is a by-product of normal muscle activity, which is found in the urine and blood; bacteria and white blood cells are signs of infection.

    New dipstick tests don't just reveal that a substance exists in the urine; they also estimate how much of the substance is there. If there are large amounts of glucose, protein, or red blood cells, it is a warning that something is wrong.
  3. Urinalysis also includes examining a small amount of urine under a microscope. Some of the things that may be seen in a microscope include:
    • Red blood cells, which may be a sign of kidney diseases that damage the filtering units of the kidneys, allowing blood cells to leak into the urine. Blood in the urine may also be a sign of problems such as kidney stones, infections, bladder cancer or a blood disorder like sickle cell disease.

    • White blood cells are a sign of an infection or inflammation in the kidneys, bladder or another area.

    • Bacteria is usually a sign of an infection in the body. Normal urine does not contain bacteria.

    • Crystals that are formed from chemicals in the urine. If they become large enough, they form kidney stones.

    Urinalysis doesn't answer all the questions about your health. It provides a clue. In fact, it can lead to more tests to understand what is happening. Protein in the urine is a sign of kidney disease. But a normal urinalysis does not guarantee that you do not have chronic kidney disease. Some people will not release a significant amount of protein early in a disease process. Or, they may release protein only occasionally, so it is missed by a single urine sample. In someone who has ingested large amounts of water, making larger amounts of urine, small quantities of chemicals may be undetectable. So, when you are asked to “pee in the cup,” you now know how important it can be to your medical care!