The kidneys take out waste material, minerals, fluids, and other substances from the blood to be passed in the urine. Urine has hundreds of different body wastes. What you eat, drink, how much you exercise, and how well your kidneys work can affect what is in your urine. More than 100 different tests can be done on urine.
A regular urinalysis often includes the following tests.
- Colour. Many things affect urine color, including fluid balance, diet, medicines and diseases. How dark or light the color is tells you how much water is in it. Vitamin B supplements can turn urine bright yellow. Some medicines, blackberries, beets, rhubarb, or blood in the urine can turn urine red-brown.
- Clarity. Urine is normally clear. Bacteria, blood, sperm, crystals, or mucus can make urine look cloudy.
- Odour. Urine does not smell very strong, but has a slightly "nutty" odour. Some diseases cause a change in the odour of urine. For example, an infection with E. coli bacteria can cause a bad odour, while diabetes or starvation can cause a sweet, fruity odour.
- Specific gravity. This checks the amount of substances in the urine. It also shows how well the kidneys balance the amount of water in urine. The higher the specific gravity, the more solid material is in the urine. When you drink a lot of fluid, your kidneys make urine with a high amount of water in it which has a low specific gravity. When you do not drink fluids, your kidneys make urine with a small amount of water in it which has a high specific gravity.
- pH. 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. Sometimes the pH of urine is affected by certain treatments. For example, your doctor may instruct you how to keep your urine either acidic or alkaline to prevent some types of kidney stones from forming.
- Protein. Protein is normally not found in the urine. Fever, hard exercise, pregnancy, and some diseases, especially kidney disease, may cause protein to be in the urine.
- Glucose. Glucose is the type of sugar found in blood. Normally there is very little or no glucose in urine. When the blood sugar level is very high, as in uncontrolled diabetes, the sugar spills over into the urine. Glucose can also be found in urine when the kidneys are damaged or diseased.
- Nitrites. Bacteria that cause a urinary tract infection (UTI) make an enzyme that changes urinary nitrates to nitrites. Nitrites in urine show a UTI is present.
- Leukocyte esterase (WBC esterase). Leukocyte esterase shows leukocytes (white blood cells [WBCs]) in the urine. WBCs in the urine may mean a UTI is present.
- Ketones. When fat is broken down for energy, the body makes substances called ketones (or ketone bodies). These are passed in the urine. Large amounts of ketones in the urine may mean a very serious condition, diabetic ketoacidosis, is present. A diet low in sugars and starches (carbohydrates), starvation, or severe vomiting may also cause ketones to be in the urine.
- Microscopic analysis. In this test, urine is spun in a special machine (centrifuge) so the solid materials (sediment) settle at the bottom. The sediment is spread on a slide and looked at under a microscope. Things that may be seen on the slide include:
- Red or white blood cells. Blood cells are not found in urine normally. 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 the urine. White blood cells may be a sign of infection 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 then get flushed out in the urine. Casts can be made of red or white blood cells, waxy or fatty substances, or protein. The type of cast in the urine can help show what type of kidney disease may be present.
- Crystals. Healthy people often have only a few crystals in their urine. A large number of crystals, or certain types of crystals, may mean kidney stones are present or there is a problem with how the body is using food (metabolism).
- Bacteria, yeast cells, or parasites. There are no bacteria, yeast cells, or parasites in urine normally. If these are present, it can mean you have an infection.
- Squamous cells. The presence of squamous cells may mean that the sample is not as pure as it needs to be. These cells do not mean there is a medical problem, but your doctor may ask that you give another urine sample.