Clinical urine tests
Clinical urine tests are examinations of the physical and chemical properties of urine and its microscopic appearance to aid in medical diagnosis. The term urinalysis—a portmanteau of the words "urine" and "analysis"—generally refers to the gross (macroscopic) examination of the urine, chemical evaluation using urine test strips, and microscopic examination. Macroscopic examination targets parameters that can be measured with the naked eye (or other senses), including volume, color, transparency, odor, and specific gravity; urine test strips measure chemical properties such as pH, glucose concentration, and protein levels; and light microscopy is performed to identify elements such  as cells, urinary casts, crystals, and organisms. Other analyses routinely performed on urine samples include urine electrolyte levels, drug testing, pregnancy testing and microbiological culture. Methods. Urinalysis. Urinalysis involves assessment of the physical properties of urine, such as color and clarity; chemical analysis using a urine test strip; and microscopic examination. Microscopic examination is not always included: it may be reserved for samples that have abnormal results on preliminary examinations, or performed at the healthcare provider's request. Test strips contain pads impregnated with chemical compounds that change color when they interact with specific elements in the urine; for example , nitrite, a compound produced by some bacteria that cause urinary tract infections, and leukocyte esterase, an enzyme found in white blood cells (WBCs) which acts as an indicator of the number of WBCs in the urine. The intensity of the color change correlates roughly with the concentration of each compound. If microscopy is necessary, the urine is first centrifuged to concentrate the solid elements so that they can be viewed more easily. A drop of the concentrated sample is placed under a coverslip and examined, typically at 10x and 40x magnification. If it is necessary to determine the exact number  of cells or casts in the sample, it can be placed in a counting chamber called a hemocytometer. Urine is traditionally examined by light microscopy, but some laboratories use phase-contrast microscopes, which improve the visualization of elements such as urinary casts and mucus. There are also automated systems that use fluorescence flow cytometry technology and others with pattern recognition to identify microscopic elements in the urine. Urine test strip. A urine test strip can quantify: Microscopic examination. The numbers and types of cells and/or material such as urinary casts can yield a great detail of information and may suggest  a specific diagnosis. Target parameters. Urine test results should always be interpreted using the reference range provided by the laboratory that performed the test, or using information provided by the test strip/device manufacturer. Color. The following are examples of some urine colors and their causes (not a complete listing). Smell. The odor (scent) of urine can normally vary from odorless (when very light colored and dilute) to a much stronger odor when the subject is dehydrated and the urine is concentrated. Brief changes in odor are usually merely interesting and not medically significant. (Example: the abnormal smell many people  can detect after eating asparagus.) The urine of diabetics experiencing ketoacidosis (urine containing high levels of ketone bodies) may have a fruity or sweet smell. Ions and trace minerals. A sodium-related parameter is fractional sodium excretion, which is the percentage of the sodium filtered by the kidney which is excreted in the urine. It is a useful parameter in acute kidney failure and oliguria, with a value below 1% indicating a prerenal disease and a value above 3% indicating acute tubular necrosis or other kidney damage. Drugs. Urine may be tested to determine whether an individual has engaged in  recreational drug use. In this case, the urinalysis would be designed to detect whatever marker indicates drug use. History. Helen Murray Free and her husband, Alfred Free, pioneered dry reagent urinalysis, resulting in the 1956 development of Clinistix (also known as Clinistrip), the first dip-and-read test for glucose in urine for patients with diabetes. This breakthrough led to additional dip-and-read tests for proteins and other substances. The invention was named a National Historic Chemical Landmark by the American Chemical Society in May 2010.