David Slotnick, M.D.
A urine test, or urinalysis, uses a sample of urine to diagnose diseases of the urinary system and other body systems. It is used to check for early signs of a disease or disorder, including infections such as urinary tract infections or kidney infections.
There are many kinds of urine tests that can be used to detect infection, to monitor various inflammatory illnesses and to diagnose complications. Urine tests used specifically to detect the nature of infectious diseases include nitrate tests and white blood cell tests.
Most urine tests require little preparation. However, it is important that patients clean areas near the urinary opening prior to testing because these areas host bacteria that can contaminate the urine sample, making it unusable for analysis.
Initial methods of urinalysis typically are performed in a physician’s office or laboratory and usually take just a few minutes to perform. After a sample of urine has been obtained, it is visually and chemically examined for abnormalities. If such abnormalities are present, the sample may undergo more rigorous testing such as microscopic examination or culture. In some cases, tests results are considered “positive” if a certain substance is found and “negative” if the substance is not found. In other cases, an individual’s test results must be compared against a reference range that helps determine what is considered normal and abnormal. These reference ranges may differ from lab to lab.
About urine tests
A urine test, or urinalysis, uses a sample of urine to diagnose diseases of the urinary system and other body systems. Urinalysis may be ordered to check for early signs of a disease or disorder, or it may be used to monitor chronic kidney or liver diseases. It also is used to identify the nature of many infections, such as urinary tract infections, kidney infections and certain sexually transmitted diseases (e.g., gonorrhea, chlamydia).
The kidneys filter wastes and byproducts of metabolism from the blood, and regulate the amount of water in the body. They also conserve compounds such as proteins and electrolytes that the body can reuse. All filtered material and water not needed moves from the kidneys to the bladder is excreted in urine. Many illnesses and other disorders cause abnormalities to appear in a person’s urine. Testing a person’s urine may reveal substances that usually are not found in large amounts in the urine, including glucose, protein, bilirubin, red blood cells, white blood cells, crystals and bacteria. Bacteria are especially indicative of the presence of an infection within the body.
Urine testing is a simple and easy method of detecting some potentially serious conditions.. In addition, urine tests serve a number of purposes, such as:
- Revealing the presence of various infections. Urine tests are used to detect the presence of urinary tract infections, in which bacteria (especially E. coli) moves from the skin outside the urethra into the urinary tract. This results in painful urination. Left untreated, a urinary tract infection can spread to and infect the kidneys and possibly enter the bloodstream. This latter type of infection is known as sepsis, and it may cause fever, chills and fatigue. Urine tests may also reveal the presence of the DNA or genes of bacteria that can cause certain sexually transmitted diseases.
- Monitoring for or detecting the presence of substances in urine (e.g., blood, proteins, creatinine) that indicate kidney disease or diabetes.
- Assessing levels of minerals to help diagnose diseases. For example, elevated levels of calcium in urine can suggest certain types of cancer. Below-normal amounts of phosphate in urine can indicate osteomalacia (a painful condition characterized by weakened bones) or kidney diseases.
- Finding tumor markers. Several tumor markers, including an enzyme called telomerase, may reveal bladder cancer. A recently discovered tumor marker called thymosin beta-15 may indicate prostate cancer or, in a patient diagnosed with prostate cancer, a more aggressive form of the disease.
- Revealing pregnancy. Home pregnancy tests use urine samples and can usually detect pregnancy about two weeks after conception.
- Indicating menopause. The U.S. Food and Drug Administration (FDA) has approved a home urine test kit that measures follicle stimulating hormone (FSH) and may show that a woman is in or about to enter menopause.
Different urine tests may require different methods of analysis. Initial methods of urinalysis are performed in a physician’s office or laboratory and usually take just a few minutes to perform. They include:
- Visual examination. Tester visually examines the color, concentration and clarity of the urine sample. Blood may make the urine appear red or brown. An infection may cause the sample to appear cloudy.
- Test strip examination (chemical examination). Tester uses a chemically-coated test strip to measure the amount of certain substances in the urine, including blood, glucose, creatinine, protein, pH, nitrite, ketones and bilirubin. The test strip is dipped into the urine sample. A chemically coated test pad on the strip will react with the urine and change color accordingly. The test pad is then compared to a color chart of possible results. Test times vary, but most test strips provide results in less than a minute.
When an abnormality is discovered during the visual or test strip examination, the sample may be sent to a laboratory for additional testing. Such testing includes:
- Microscopic examination. The tester examines a small amount of urine under a microscope. Cells, bacteria, mucus, casts (protein substances that can indicate kidney disorders), crystals and other matter are counted and reported as either the number observed or as estimates (e.g., few, moderate or many).
- Culture. When the presence of bacteria is suspected in the urine, a urine culture may be ordered. A sample of urine is streaked across the surface of one or more lab dishes (Petri dish). The sample is then placed in an incubator that keeps the urine at body temperature. Bacteria will be allowed to grow in the dish so the type of bacteria can be determined. If there is no growth on the dish at the end of 24 hours, the test is considered negative for infection. If yeast or bacteria are present, the organisms are identified and counted. In some cases, more than one type of bacteria may be present. This usually indicates the presence of an infection that involves more than one disease-causing microorganism (pathogen). When a culture reveals the presence of bacteria, further testing is conducted to determine which antibiotics are likely to be effective in treating the infection and to keep it from spreading to other parts of the body.
The results of urine tests are typically used as a warning sign to indicate the presence of illness or the need to monitor a potentially developing health problem. In most cases, the greater the concentration of an abnormal substance, the increased likelihood that a health problem exists. However, it is important to note that urine tests cannot detect all conditions, and that a normal urine test does not necessarily indicate that a person is healthy.
Types and differences of urine tests
There are many kinds of urine tests that can be used to detect infection, to monitor various inflammatory illnesses and to diagnose complications.
Urine tests used specifically to detect the nature of infectious diseases include:
- Nitrite test. Nitrite is normally not detectable in the urine. Nitrite is formed when bacteria changes nitrate in the urine into nitrite. The presence of nitrite in the urine (nitrituria) is often a sign of a urinary tract infection.
- White blood cell test. Checks urine for the presence of white blood cells. The main infection-fighting cells in the body, white blood cells are not normally detectable in the urine. The presence of white blood cells in the urine may indicate a urinary tract infection or prostatitis.
Other types of urine tests include:
- Uric acid test. Uric acid is the end product of the breakdown of nucleotides as a normal part of metabolism. In conjunction with urinalysis of other waste products, it can be used to assess how well the kidneys are functioning. It is a common diagnostic test for gout, a form of arthritis caused by excessive amounts of uric acid in the blood and deposits of excess uric acid crystals (urates) in and around the joints.
- Creatinine test. Measures the amount of creatinine in the urine. Creatinine is a waste product removed from the body by the kidneys. Abnormal amounts of creatinine may be a sign of kidney damage. Urinalysis for this waste product is commonly ordered in patients who have inflammatory diseases, such as lupus and scleroderma, to monitor for kidney damage. Creatinine is sometimes checked with a creatinine clearance test. This compares results of a blood test to a 24-hour urine sample.
- Bilirubin test. Measures the amount of bilirubin – an orange-yellow waste product made from damaged or old red blood cells that have died – in the urine. Bilirubin is normally not detected in the urine. Excessive amounts of bilirubin can cause jaundice (yellowing of the skin and the whites of the eyes).
- Microalbuminuria test. Detects albumin, a protein that prevents fluid from leaking out of blood vessels, nourishes tissues and transports vitamins, hormones, drugs and ions throughout the body. Protein is not normally detectable in urine. The presence of protein in urine (proteinuria) is often an early sign of kidney disease. People with diabetes or inflammatory diseases such as lupus and scleroderma should be regularly tested for microalbuminuria for early detection and prevention of kidney damage.
- Urine specific gravity test. Measures the concentration of particles in the urine. Abnormally increased or decreased urine specific gravity may indicate a kidney disorder.
- Urine pH test. Measures the pH (acidity) of the urine. A high level of urine pH may indicate a kidney disorder, including kidney failure.
Before, during and after the urine test
Prior to the urine test, a physician will ask questions about the patient’s medical history to determine if the patient is taking any medications or vitamins that will interfere with the test’s results.
Most urine tests require little preparation. The physician may instruct the patient to restrict exercise and to reduce or stop taking certain medications or vitamins at some point prior to the test.
Many urine tests involve only a spot (single) sample (also called a dipstick method) in which patients collect their urine samples in a physician’s office or clinic. Patients receive a cup or other container that they take into the bathroom. To capture a sample of urine, patients should try to obtain the specimen in midstream, a technique known as “clean-catch.” Preparation for this technique differs depending on the patient’s sex:
- Males. Wipe clean the head of the penis
- Females. Wash the area between the lips of the vagina with soapy water and rinse well.
It is important to clean these areas, because the urinary opening hosts bacteria that can contaminate the urine sample, making it unusable for analysis.
Patients should not use the first sample upon awakening, but should instead wait to take a later sample. At least three hours should expire between the previous void and the episode used for obtaining the sample. As patients start to urinate, they should let a small amount of the initial urine fall into the toilet bowl. This will help clear theurethra of contaminants. Using a clean container, patients should capture between 1 and 2 ounces (between 30 and 60 milliliters) of urine before removing the container and finishing urinating into the toilet bowl.
After patients have cleansed, they should give the container and sample to a healthcare provider or assistant.
When obtaining a sample from an infant, an adult should prepare the child by washing the area around the urethral opening. Because infants cannot give voluntary samples, parents will have to rely on a urine collection bag to obtain the sample. This is a plastic bag with an adhesive paper on one end. For boys, the bag is placed over the penis and the adhesive is attached to the skin. For girls, the bag is placed over the labia. The child then wears a diaper over the bag.
The child’s caregiver will need to check frequently to see if the infant has urinated into the bag. After the urine has been obtained, it is poured into a container and brought to a healthcare provider.
Some urine tests, such as those performed to measure levels of certain waste products (e.g., uric acid, bilirubin, creatinine) require a 24-hour sample rather than a spot sample. This is a collection of urine over a 24-hour period. To collect such a sample, the patient should:
- Get up in the morning of the first day of the test and empty the bladder. The urine should then be discarded in the toilet.
- Collect all subsequent urine in the provided container for the next 24 hours.
- Cap the container and keep it in a refrigerator or cool place during the collection period.
- Get up in the morning of the second day of the test and urinate into the container.
- Return the container to the physician’s office or a laboratory for analysis.
Afterward patients may resume exercise, medication and vitamin intake according to their physician’s instructions.
Other types of samples include an overnight urine sample (collection of all urine excreted between going to sleep at night and waking up in the morning) and a timed urine sample (collection of all urine voided in a specific period of time).
It typically takes two or three days for a laboratory to complete a urinalysis. A pathologist will use a microscope to examine the sample for signs of disease, such as bacteria, abnormal epithelial cells (which may indicate cancer), excessive numbers of red blood cells, white blood cells or other abnormal cells. In addition, physicians may order additional tests, such as blood tests, a biopsy, x-rays or an MRI, to verify a diagnosis. Treatment depends on the condition that is diagnosed.
Understanding test results
In some cases, tests results are considered “positive” if a certain substance is found and “negative” if the substance is not found. For example, the presence of certain antibodies to a particular type of disease or other substances in a urine sample may indicate a patient has a certain type of infection.
However, other urine tests require that an individual’s test results be compared against a reference range that helps determine what is considered normal and abnormal. To establish these ranges, a large number of healthy people are first tested. The results of those tests are then used to help determine a “normal” range for the substance that is being tested.
For example, urine testing is sometimes performed to discover the creatinine content in a patient’s urine. In order to determine whether the patient’s level is normal or abnormal, the patient’s sample must be compared to creatinine levels expected in healthy individuals.
In addition, key demographic characteristics often must be taken into account when comparing an individual’s results against a reference range. For example, men have higher creatinine levels than women. Therefore, a sample obtained from a male must be compared to the reference range for males rather than females.
Factors often taken into account when establishing reference ranges include age, gender, pregnancy and lifestyle factors (e.g., smoking, diet). In addition, individual laboratories often establish their own reference ranges to reflect factors such as the type of equipment and testing methods they use.
For this reason, organizations such as the American Association for Clinical Chemistry urge patients and physicians to follow the individual laboratory’s interpretation of results rather than comparing the results to published reference ranges.
Results that fall outside of a reference range often – but not always – indicate a potential health problem. Some healthy people have results that nonetheless fall outside the reference range. For this reason, physicians treat abnormal test results as a signal that more testing is needed rather than as confirmation of an illness.
It should also be noted that results that fall within the reference range do not necessarily guarantee that a person is healthy. In some cases, a physician may want to perform additional tests to confirm that an individual is healthy.
Questions for your doctor regarding urine tests
Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about urine tests:
- What type of urine test is recommended for me?
- What does my test involve?
- When is the best time to obtain my urine sample?
- Do I have to avoid any foods or stop any medication?
- What should I do to ensure accurate results?
- How long will it take to get the results of my urine test?
- What will I learn from the urine test?
- Will I need additional tests to confirm diagnosis?
- What is the recommended treatment for my condition?
- Do I need urinalysis regularly to monitor my condition?