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Urinalysis DISCUSSION The Kidneys Urine, a metabolic waste product, is produced in the kidneys, two bean-shaped organs located on either side of the spine just above the waistline. The kidneys are well protected from bruising by a thick capsule of fat. The kidneys, along with the skin and lungs, are excretory organs. The kidneys function as filters of the blood. Approximately one-fourth of all the blood from the heart flows to the kidneys through the large renal arteries. Substances in the blood are either retained or filtered out into the urine through a capillary network. The kidneys can either concentrate or dilute the urine with these waste substances, thus balancing the body's internal environment. Urine passes through tubules in the kidneys to the ureter, which leads to the urinary bladder, a storage organ. Stored urine is then voided through the urethra. Our lives depend upon the proper functioning of the kidneys and urinary system. The functional state of the kidneys can be assessed by physical, chemical, or microscopic examination of the urine (urinalysis), which has been practiced by doctors for over 5000 years. Before modern techniques were developed, doctors used appearance, odor, and taste of urine as indicators of health and disease. Today urinalysis is used to diagnose kidney disease, to follow the treatment of kidney disease, and to diagnose other disorders that affect the kidneys. Urine Tests Normally, urine consists of 95% water and 5% solids such as urea and sodium chloride. Almost all substances found in urine are also found in blood but at different concentrations. Some substances such as glucose have a renal threshold that must be exceeded before the substance is excreted. Presence of such substances in the urine usually indicates disease. This exercise teaches five important tests routinely done in clinical urinalysis: color, pH, specific gravity, glucose, and protein. MATERIALS 10-ml graduated cylinder Clinitest Tablets with Chart Urine Specimen Containers Glass Vials Jumbo pH Strips, Wide Range Biuret Reagent Urine Hydrometer and Jar Sets Pipets * Because urine may contain bacteria, thorough hand washing is needed at the completion of the exercise * PROCEDURES Color Normal urine colors range from light yellow to amber, depending upon the concentration of urochrome, the urinary pigment. Lighter or darker urine can be caused by foods, drugs, or diseases (Table 2). 1) Obtain a specimen container and collect a fresh urine specimen of approximately 25 ml. 2) Record the color of your urine specimen in Table 1 (Urine Test Results). Table 2 lists normal and abnormal urine colors and possible causes. pH The pH of a solution is a measure of the free hydrogen ion (H+) concentration, which indicates acidity or alkalinity. A solution with a pH of 7.0 is neutral, one with a pH less than 7.0 is acidic, and one with a pH greater than 7.0 is alkaline. The pH of normal urine averages 6.0, which is slightly acidic. Foods and diseases that can affect urine pH are listed in Table 3. 1) Obtain a pH indicator strip and test your urine by dipping the pH strip into it three consecutive times. 2) Shake off excess urine and closely compare the color of the strip to the colors on the pH chart. The color that most closely matches your strip corresponds to your pH. 3) Record your pH in Table 1. Specific Gravity Specific gravity is the density of a solution compared to water, which has a specific gravity of 1.000. The specific gravity of normal urine ranges from 1.010 to 1.025. Specific gravity varies according to fluid intake and can also be affected by diseases (Table 3). 1) Obtain the urine hydrometer and jar and rinse both pieces well. Fill the jar 3/4 full of urine. Place the hydrometer in the jar so that it is not touching the sides and read the level of urine on the hydrometer scale. Record your measured (base) urine specific gravity in Table 1. 2) Remove the hydrometer and pour your urine back into the specimen container. 3) Wash the jar and hydrometer well with soap and water. Glucose Glucose (sugar) should not be detected in normal urine. The presence of glucose usually indicates diabetes mellitus, a severe metabolic disorder due to defective carbohydrate utilization. See Table 3 for causes of glucose in the urine. 1) Using a dropping pipet, place 5 drops of urine into a glass vial. 2) Rinse the dropper thoroughly with water and add 10 drops of water to the vial. 3) Drop one Clinitest tablet into the vial. Place the vial on the tabletop and observe the reaction. Caution: the glass vial will become very hot during the chemical reaction. 4) After the reaction has stopped, wait 15 seconds. Shake the vial gently to mix the contents. Compare the color to the Clinitest color chart. Caution: do not allow the contents of the vial to come into contact with your skin or eyes. 5) Record the results of the test for glucose (positive or negative) in Table 1. Protein A very small amount of protein is normally present in the urine. The biuret reagent causes a color change in the presence of excessive protein. Both diet and disease can affect protein level in the urine. Factors associated with excretion of protein into the urine are listed in Table 3. 1) Using a 10-ml graduated cylinder, add 1 ml urine to a clean glass vial. 2) Rinse the graduated cylinder and measure 2 ml biuret reagent (note the pale blue color of the biuret reagent). 3) Add the biuret reagent to the urine vial. 4) Gently swirl the vial to mix the contents. After 10 minutes hold the test tube against a white background and observe the color. A color change from light blue to pale violet indicates the presence of protein. 5) Record the results of the test for protein (positive or negative) in Table 1. Table 2 Urine Colors and Possible Causes Color Diet Drugs Disease Light yellow to amber Normal Uncontrolled diabetes Clear to light yellow Alcohol Phosphate, carbonate mellitus Yellow orange to dark Bilirubin from obstructive Carrots Antibiotics green jaundice Red to red brown Beets Laxatives Hemoglobin in urine Unhemolyzed red blood Smokey red Beets Anticonvulsants cells from urinary tract Dark wine Beets Anti-inflammatory drugs Hemolytic jaundice Melanin pigment from Brown black Rhubarb Antidepressants melanoma Brown Rhubarb Barbiturates Anemia or liver infections Green Green food dyes Diuretics Bacterial infection Table 3 Abnormal Urinalysis Results and Possible Causes Test Result Diet Disease High protein diet, Uncontrolled diabetes Low pH (<4.5) cranberry juice mellitus Diet rich in vegetables, High pH (>8.0) Severe anemia dairy products Low Specific Gravity (<1.010) Increased fluid intake Severe renal damage Decreased fluid intake, Uncontrolled diabetes High Specific Gravity (>1.025) loss of fluids mellitus, severe anemia Uncontrolled diabetes Glucose Present Large meal mellitus, severe anemia Protein Present Protein diet Severe anemia Names _____________________________ Urinalysis _____________________________ Period _____ Table 1 Urine Test Student Results Normal Results Color Yellow to amber pH 4.6-8.0 Specific gravity 1.010-1.025 Glucose Negative Protein Negative QUESTIONS 1) Are your urinalysis results normal? If not, which tests were abnormal and what might this indicate? 2) The following abnormal results were obtained from a patient's urinalysis: Color: very light yellow Glucose: positive pH: 3.0 Protein: negative Specific gravity: 1.040 Name a disease that could cause these results.
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