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Urinalysis Urine is produced by the kidney to maintain constant plasma osmotic concentration; to regulate pH, electrolyte and fluid balances and to excrete some 50 grams of waste solids (mostly urea and sodium chloride). Some normal urine constituents excreted (in g/24 hours): Urea Uric acid Creatinine Hippuric acid Ammonia Amino acids Sodium Potassium Calcium Magnesium Chloride Phosphate Sulfate 25-30 0.6-0.7 1.0-1.2 0.7 0.7 3 1-5 (NaCl 15.0) 2-4 0.2-0.3 0.1 7 1.7-2.5 1.8-2.5 Routine urinalysi
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  Urinalysis Urine is produced by the kidney to maintain constant plasma osmoticconcentration; to regulate pH, electrolyte and fluid balances and to excrete some 50grams of waste solids (mostly urea and sodium chloride).Some normal urine constituents excreted (in g/24 hours): Urea 25-30Uric acid 0.6-0.7Creatinine 1.0-1.2Hippuric acid 0.7Ammonia 0.7Amino acids 3Sodium 1-5 (NaCl 15.0)Potassium 2-4Calcium 0.2-0.3Magnesium 0.1Chloride 7Phosphate 1.7-2.5Sulfate 1.8-2.5Routine urinalysis is composed of two examinations:1) Chemical tests for abnormal chemical constituents2) Microscopic exam for abnormal insoluble constituents PROCEDURESThe color and appearance of the urine specimen is recorded. Usual colors arecolorless, straw, yellow, amber; less commonly pink, red, brown. Usual appearances(opacity) are clear or hazy; less commonly turbid, cloudy and opaque, unless thespecimen has remained at room or refrigerated temperatures. A fresh urine specimen is collected in a clean, dry container. A Multistix stripis briefly immersed in the urine specimen, covering all reagent areas.The edge of the Multistix strip is run against the rim of the urine container toremove excess urine. The strip is held in a horizontal position.  The reactions are read visually or automatically with a Clinitek reflectionphotometer. If the strip is evaluated visually, the strip test areas are comparedto those on the Multistix color chart at the specified times. The results arerecorded, and the strip is discarded.   METHODOLOGIES AND INTERPRETATIONSGlucose:This test is based on a double sequential enzyme reaction. One enzyme,glucose oxidase, catalyzes the formation of gluconic acid and hydrogenperoxide from the oxidation of glucose. A second enzyme, peroxidase,catalyzes the reaction of hydrogen peroxide with a potassium iodidechromogen to oxidize the chromogen to colors ranging from green tobrown.In general the presence of glucose indicates that the filtered load of glucose  exceeds the maximal tubular reabsorptive capacity for glucose. In diabetesmellitus, urine testing for glucose is often substituted for blood glucosemonitoring.Bilirubin:This test is based on the coupling of bilirubin with diazotizeddichloroanaline in a strongly acid medium. The color ranges throughvarious shades of tan.Bilirubin in the urine indicates the presence of liver disease or biliaryobstruction. Very low amounts of bilirubin can be detected in the urine,even when serum levels are below the clinical detection of jaundice.Ketone:This test is based on the development of colors ranging from buff-pink, fora negative reading, to purple when acetoacetic acid reacts withnitroprusside.Urine testing only detects acetoacetic acid, not the other ketones, acetoneor beta-hydroxybuteric acid. In ketoacidosis (insulin deficiency orstarvation), it can be present in large amounts in the urine before anyelevation in plasma levels.SpecificGravity:This test is based on the apparent pKa change of certain pretreatedpolyelectrolytes, poly(methyl-vinyl-ether/maleic anhydride), in relation toionic concentration. In the presence of bromthymol blue, colors range deepblue-green in urine of low ionic concentration through green and yellow-green in urines of increasing ionic concentration.The specific gravity is a convenient index of urine concentration. Itmeasures density and is only an approximate guide to true concentration.A specific gravity of <1.010 is consistent with a concentrating defect. Aspecific gravity of >1.025, in the absence of protein, glucose and other largemolecular weight substances such as contrast media, usually indicatesnormal renal concentration and makes chronic renal insufficiency  unlikely.Blood:This test is based on the peroxidase-like activity of hemoglobin, whichcatalyzes the reaction of diisopropylbenzene dihydroperoxide and 3,3',5,5'-tetramethylbenzidine. The resulting color ranges from orange throughgreen; very high levels of blood may cause the color development tocontinue to blue.The presence of large numbers of RBCs in the urine sediment establishesthe diagnosis of hematuria. If the dipstick is more strongly positive thanwould be expected from the number of RBCs, then the possibility of hemoglobinuria or myoglobinuria should be considered.pH:The test is based on the double indicator (methyl red/bromthymol blue)principle that gives a broad range of colors covering the entire urinary pHrange. Colors range from orange through yellow and green to blue.The urine pH should be recorded, although it is seldom of diagnostic value.Phosphates will precipitate in an alkaline urine, and uric acid willprecipitate in an acidic urine.Protein:This test is based on the protein-error-of-indicators (tetrabromphenolblue) principle. At a constant pH, the development of any green color isdue to the presence of protein. Colors range from yellow for negativethrough yellow-green and green to green-blue for positive reactions.Heavy proteinuria usually represents an abnormality in the glomerularfiltration barrier. The test is more sensitive for albumin than for globulinsor hemoglobin.Urobilinogen:This test is based on the modified Ehrlich reaction, in which para-
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