The first morning specimen of urine is moreconcentrated and will have a higher specific gravitythan a specimen passed during the day. A high fluidintake may reduce the specific gravity to below 1.010.In the presence of disease, the specific gravity of a24-hour specimen may vary from 1.001 to 1.060.Specific gravity is measured with an indexrefractometer, available as standard equipment at mostduty stations. See figure 7-22. The index refracto-meter may be held manually or mounted on a stand likea microscope. The specific gravity of urine isdetermined by the index of light refraction throughsolid material.Measure the specific gravity with an indexrefractometer in the following manner:1. Hold the index refractometer in one hand. Usethe other hand and an applicator stick to place adrop of urine on the glass section beneath thecoverglass.2. Hold the refractometer so that the light reflectson the glass section, and look into the ocularend. Read the number that appears where thelight and dark lines meet. This is the specificgravity.Chemical CharacteristicsChemical characteristics evaluated during aroutine urinalysis include pH, protein, glucose,ketones, and blood. Some laboratories also includetests for bilirubin, urobilinogen, and nitrite, dependingon the test strip used. Currently, most medicalfacilities use the Multistix® and Color Chart, whichdetects pH, protein, glucose, ketones, blood, bilirubin,and urobilinogen. The Multistix is a speciallyprepared multitest strip. The strip is simply dippedinto the urine specimen and compared to the colorvalues for the various tests on the accompanying chart.The color chart also indicates numerical pH values,which should be reported.Microscopic Examination of Urine SedimentMicroscopic examination of urine sediment isusually performed in addition to routine procedures.This examination requires a degree of skill acquiredthrough practice under the immediate supervision ofan experienced technician. The specimen used formicroscopic examination should be as fresh aspossible. Red cells and many formed solids tend todisintegrate upon standing, particularly if thespecimen is warm or alkaline.PREPARING SPECIMENS FOR MICRO-SCOPIC EXAMINATION.—To prepare urinespecimens for microscopic examination, follow thesteps below.1. Stir the specimen well.2. Pour 15 ml of urine into a conical centrifugetube, and centrifuge at 1,500 rpm for 5 minutes.3. Invert the centrifuge tube and allow all of theexcess urine to drain out. Do not shake the tubewhile it is inverted. Enough urine will remainin the tube to resuspend the sediment. Too muchurine will cause dilution of the sediment,making an accurate reading difficult.4. Resuspend the sediment by tapping the bottomof the tube.5. With a medicine dropper, mount one drop of thesuspension on a slide and cover it with acoverslip.6. Place the slide under the microscope, and scanwith the low-power objective and subduedlighting.7. Switch to the high-power objective for detailedexamination of a minimum of 10 to 15 fields.CLINICALLY SIGNIFICANT FINDINGS.—Leukocytes, erythrocytes, and casts may all be ofclinical significance when found in urine sediment.Leukocytes.—Normally, 0 to 3 leukocytes perhigh-power field will be seen on microscopicexamination. More than 3 cells per high-power fieldprobably indicates disease somewhere in the urinarytract. Estimate the number of leukocytes present perhigh-power field and report it as the “estimatednumber per high-power field.”Erythrocytes.—Red cells are not usually presentin normal urine. If erythrocytes are found, estimatetheir number per high-power field and report it.Erythrocytes may be differentiated from white cells inseveral ways:White cells are larger than red cells.7-35HM3f0722Figure 7-22.—Index refractometer.
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