Urinalysis
Examining urine for signs of disease has been recommended since at least the time of Hippocrates, the father of Western medicine, who told his followers to check urine color in those who were sick.

Kidneys act as filters for the bloodstream, purifying all the blood as it passes through them. The kidneys filter the equivalent of about 150 quarts of blood that recyles daily. The kidneys remove wastes and ensure that needed substances are left in the blood. Urine is produced by the kidneys when they remove soluble waste products from the body. Kidneys, like most of the organs of the body, perform a number of functions. Among their biological roles, kidneys help control blood pressure and synthesize an active form of vitamin D.

A urinalysis is most often ordered if a urinary tract infection is suspected, although there are other reasons why such a test could be useful. Like the complete blood count, a urinalysis can check on several different things:

• The number and kind of cells from the lining of the kidneys and bladder that have appeared in the urine
• The number and variety of both red (RBCs) and white blood cells (WBCs)
• The presence of bacteria or other organisms
• A variety of chemicals that the kidneys filter (when healthy or sick), such as glucose
• The pH, measuring how acidic or basic the urine is
• The concentration of the urine.

Sometimes results that may seem abnormal, such as the presence of white or red cells in the urine, may be the result of how or when the urine was collected rather than disease. For example, a dehydrated, crying child may have a few RBCs or WBCs in the urine. Once she is rehydrated, these "abnormal" results may disappear.