urinalysis (yŏrˌənălˈĭsĭs) [key], clinical examination of urine for the purpose of medical diagnosis. Urine is initially examined for such characteristics as color, odor, and specific gravity. It is routinely tested for acidity, as indicated by its p H reading, and screened for sugar, ketone bodies, proteins, and bile content. Benedict's solution, for example, may be used to test for simple sugars, a high level of which is a possible indicator of diabetes mellitus. Ketone bodies, e.g., acetone and acetoacetic acid, in the urine indicate the substitution of fats for sugar in the energy cycle and are another indication of diabetes mellitus. Abnormal levels of protein may be signs of kidney disease. A high concentration of bile in the urine is a sign of liver malfunction or blockage of the bile duct. Urine is examined microscopically to determine blood count. High levels of erythrocytes, or red blood cells, and leukocytes, or white blood cells, may be a result of bleeding and infection, respectively, in the urinary tract. Casts, crystals, and other substances, whose origins may be ascertained by determining their chemical structures, can be observed microscopically. Additional studies are performed when specific malfunctions are suspected. Clearance tests, for instance, will determine the ability of the kidneys to remove waste substances from the blood plasma per unit of time. The urine of patients with melanotic cancer will often contain melanin, a skin pigment. A diagnosis of drug addiction may be confirmed by the presence of specific chemical substances in the urine. Urinalysis is also employed to test for pregnancy. Pregnant women secrete high levels of gonadotrophic, or ovary-regulating, hormones from the placenta. A reagent containing gonadotrophic hormones is mixed with a sample of urine from the patient, and gonadotrophic antigens are added to it. Failure of the antigens to clump, or agglutinate, is positive evidence of pregnancy.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.