General Urine Test - Points To Note
Tests on urine provide information and clues to many diseases, and can also be indications of the condition of a patient's health. A routine urine-screening test may be done to help find the cause for a number of different symptoms.
The kidneys remove waste material, minerals, fluids, and other substances from the blood for elimination through urine. Therefore, urine can contain hundreds of different bodily waste products. Many factors (such as diet, fluid intake, exercise, and kidney function) affect the constituents of urine. Over 100 different tests can be done on urine. However, a routine urinalysis usually involves the following tests.
Many factors affect the color of urine, including fluid balance, diet, medications and disease. The intensity of the color generally indicates the concentration of the urine; pale or colorless urine indicates that the urine is dilute, and deep yellow urine indicates that it is concentrated. Vitamin B supplements can turn urine bright yellow. Reddish brown urine is usually caused by certain medications, eating blackberries or beets or by the presence of blood in urine.
This test (also called opacity or turbidity) determines the cloudiness of the urine. Urine is normally clear, but bacteria, blood, sperm, crystals, or mucus can make urine appear cloudy.
Some diseases cause a change in the normal odor of urine. For example, an infection with E. coli bacteria can cause a foul odor while diabetes or starvation can cause a sweet, fruity odor.
Specific gravity measures the amount of substances dissolved in the urine. It also indicates how well the kidneys are able to adjust the amount of water in urine. The higher the specific gravity, the more the solid material dissolved in the urine. When a person drinks a lot of liquids, the kidneys generally produce greater than normal amounts of dilute urine. When a person drinks very little liquid, the kidneys generally make only small amounts of concentrated urine.
The pH is a measure of how acidic or alkaline (basic) the urine is. A urine pH of 4 is strongly acidic, 7 is neutral (neither acidic nor alkaline), and 9 is strongly alkaline. Certain types of treatment sometimes adjust the pH of the urine. For example, efforts are made to keep urine either acidic or alkaline to prevent formation of certain types of kidney stones.
Normally there is no protein in the urine. Sometimes a small amount of protein is released into the urine when a person stands up (this condition is called postural proteinuria). Fever, strenuous exercise, normal pregnancy, and some diseases (especially kidney disease) may also cause protein in the urine.
Glucose is the type of sugar usually found in blood. Normally there is very little or no glucose in urine. However, when the blood sugar level is very high, as in uncontrolled diabetes, it spills over into the urine. Glucose can also be present in urine when the kidneys are damaged or diseased.
When fat is broken down for energy, the body produces by-products called ketones (or ketone bodies) and releases them into the urine. Large amounts of ketones in the urine may signal a dangerous condition known as Diabetic Ketoacidosis. A diet low in sugars and starches (carbohydrates), starvation, or prolonged vomiting may also cause ketones in the urine.
In this test, urine is spun in a centrifuge so the solid materials (sediment) settle out. The sediment is spread on a slide and examined under a microscope. The materials that may be found include:
- Red or white blood cells. Normally blood cells are not found in urine. Inflammation, disease, or injury to the kidneys, ureters, bladder or urethra can cause blood in urine. Strenuous exercise (such as running a marathon) can also cause blood in urine. White blood cells are often a sign of infection, cancer, or kidney disease.
- Casts. Some types of kidney disease can cause plugs of material (called casts) to form in tiny tubes in the kidneys. The casts can then get flushed out into the urine. Casts can be made of different types of material, such as red or white blood cells, waxy or fatty substances, or protein. The type of cast can provide clues about the type of kidney disease that may be present in the body.
- Crystals. Healthy people often have only a few crystals in their urine. However, a large number of crystals, or the presence of certain types of crystals, may indicate kidney stones or a problem with how the body is using food (metabolism).
- Bacteria, yeast cells, or parasites. Normally there are no bacteria, yeast cells, or parasites in urine. The presence of these indicates an infection.
This test is done on a sample of urine.