Urinalysis, urine examination, is a basic diagnostic tool and valuable for any medical specialty. Urinalysis allows immediate conclusions to be drawn about a patient’s general health, particularly the condition of the kidneys and the urinary tract.
What is urinalysis?
Urinalysis allows immediate conclusions to be drawn about a patient’s general health, particularly the condition of the kidneys and urinary tract. Urine is a sterile blood serum concentrate. Urine is produced by the filtering function of the kidneys as retroperitoneal paired organs. The kidneys constantly filter the blood and rid it of toxins or metabolic products. Thus, in the course of 24 hours, about 1500 liters of primary urine become about 1.5 liters of final urine through concentration and water removal, which passes from the kidney through the ureters into the bladder. When enough final urine has accumulated in the bladder, a reflex of the bladder muscles causes urination, micturition via the urethra. This urine is then used as so-called midstream urine for examination purposes. Modern urine analysis using multiple test strips and microscopic, cytological and pathological examination goes back to the traditional urine examination of the Middle Ages. At that time, the chemical composition of urine was not yet known in detail. The color, odor and taste of the urine played an important role in the diagnosis of diseases. For example, sweet-tasting urine indicated diabetes mellitus. Today, glucose detection is performed by a chemical reaction on the field of a urine test strip, which is dipped into the urine by the physician or medical assistant.
Function, effect, and goals
The color of urine depends mainly on fluid intake but also on various foods. Beet, for example, turns the urine red. However, red coloration can also be caused by the presence of blood in the urine, a pathologic finding that always requires clarification and usually indicates inflammation of the kidneys or urinary tract. The macroscopic urine examination, as it was traditionally practiced in the Middle Ages as urine examination, is no longer common today. In addition to fluid intake, the appearance of urine can be greatly altered by medications or internal diseases and inflammation. Strongly deviating changes in appearance are documented if they are relevant to diagnosis. A urinalysis, like a blood test or medical history, is a common part of a general medical consultation. Physicians of any specialty can interpret a urinalysis, but the specialist in urology or nephrology is particularly qualified to interpret findings or to perform an extended urinalysis for specific medical questions. To determine the specific urine weight, a measuring spindle is immersed in the urine, thus the weight-volume ratio is accurately determined. It is therefore possible to determine how many dissolved components are contained in the urine sample. Concentrated urine has a higher specific gravity because it contains less water. The standard urinalysis is performed using multiple test strips, the so-called Combur test. Up to 10 different test fields are available on such a test implet. The urine analysis by means of test strips is carried out in three steps: dip, wipe, read. The test results can thus be read off and documented by visual color comparison immediately after immersion with a color scale. Important test fields are glucose, pH, blood, hemoglobin, leukocytes, nitrite, protein and urobilinogen. In the test fields, the substances dissolved in the urine cause a complicated chemical reaction that is enzymatically linked to a typical color change. For example, the yellowish initial test field turns green in the presence of blood in the urine, and the white test field takes on a pink color when it comes into contact with leukocytes in the urine. The intensity of the discoloration is considered a measure of the concentration of the pathological substance. If bacteria are present in the urine due to an inflammatory process, the nitrite test field becomes discolored if the bacteria are nitrite-forming bacteria, which are responsible for over 90 percent of all urinary tract infections.The examination with the test strip can be followed by a microscopic analysis of the so-called urine sediment. The urine sediment is obtained by centrifuging the urine. The centrifugal force causes cellular components of the urine to accumulate at the bottom of the glass tube. The supernatant urine portion is decanted. Bacteria, epithelial cells, cylinders or crystals can be analyzed in the urine sediment. Bacteria can also be grown from the sediment using a culture medium for final diagnosis and resistance determination.
Risks, side effects, and hazards
Urine is an important diagnostic tool for initial diagnosis, suspected diagnosis, diagnosis of exclusion, or follow-up of internal diseases and diseases of the urinary tract. The urine used for analysis must be as fresh as possible, because urine begins to decompose due to its biological composition only a few minutes after excretion. Only so-called medium-jet urine should be used for urinalysis. When passing urine, the patient is instructed to first discard the first portion of urine, then fill the midstream into the cup and discard the felt last third. Non-compliance may result in false positive results. In order to standardize the test strip analysis of urine, automatic reading machines are now used in large practices and laboratories. This achieves far better results than manual reading. In the case of unclear or doubtful findings, urine can also be obtained directly from the urinary bladder by suprapubic bladder puncture under sterile conditions.
