Why the Doctor Asks for a Urine Sample
A urine test is probably the best way for your health care provider to know about what's going on inside your body. Urine is a fluid made by your body. It carries wastes from your blood, and extra salt and water from your body.
Your body makes urine all day. The bladder can hold almost 2 cups of urine for 2 to 5 hours comfortably. You lose about 2 quarts of urine daily when you urinate.
Lab technicians use a specially treated "dipstick" to test your urine. The dipstick is plastic stick that has small squares covered with different chemical signals on it. Unusual amounts of certain substances in your urine can tell your health care provider that something is changing in your body.
A urine test can check for many different conditions, including minor urinary tract infections to diabetes and other more serious problems. For example, one part of the dipstick is designed to measure the specific gravity of urine. The higher the gravity, the more concentrated the urine is. Urine is usually darker (more concentrated) in the morning. This is because your body's been storing wastes all night. If your urine appears concentrated (dark) during the day, it means you probably need to drink more fluids. If you don't drink enough fluids, it makes it hard for your body to flush wastes.
The dipstick shows the different chemicals that your kidneys filter, such as glucose (sugar) or minerals. Health people generally don't have a lot of sugar in their urine. If a test shows that you have a high level of sugar in your urine, it may mean that you have diabetes or another condition that keeps your body from using blood sugar properly.
A urine test also can show that you have an infection by measuring nitrites and leukocytes. The bacteria that cause infections produce a substance that changes nitrates, which are normally present in urine, to nitrites. Leukocytes are the white blood cells that fight infection. If either one of these substances show up in a test, it may be because your body is fighting an infection in the bladder or somewhere else along the urinary tract. Red blood cells in the urine can be a sign of urinary tract or kidney disease, tumors, or other problems. Further tests are needed to confirm these results.
The dipstick also checks for protein and pH levels. Urine shouldn't contain much, if any, protein. Some perfectly normal people do have tiny amounts of protein in their urine. Low levels of protein in the urine can be a sign of early or chronic kidney disease. Really high protein levels in the urine are always a sign of kidney disease. Urine pH, which measures the acid/base balance, normally ranges between 4.5 and 8. Most people's urine pH falls between 5.5 and 6.5. Urine pH can be changed by diet, medications, and certain kidney problems.
Ketones can also be detected by dipsticks. Ketones are substances that your body makes when it uses fat instead of sugar for energy. Ketones are removed from the body in urine. Large amounts of urinary ketones are typically found in patients who don't eat a lot of vegetables and grains (carbohydrates), are starving, or have diabetes. When someone with diabetes has ketones in their urine, they have a dangerous condition called diabetic ketoacidosis.
Urine tests can also help your health care provider know if your condition is getting better or worse.
Several other tests can be done on a urine sample without the dipstick. Urine pregnancy tests at home or in the office are common. Urine tests for street drugs are done in the workplace or in a health care provider's office. In some cases, your health care provider will send a urine sample to a lab for a culture or microscopic evaluation. A urine culture can show which bacteria are causing a bladder infection. This helps your provider figure out which antibiotics will work the best. Microscope evaluation can help figure out why your kidneys aren't working right. Other tests can be very specific, such as a 24-hour urine collection for total protein, or for specific hormones.
Contact your health care provider if you have any new urinary symptoms or changes in your urine.
- MMI board-certified, academically affiliated clinician
- Sather, Rita, RN