Microscopic Examination of Urine Sediment

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The first morning specimen of urine is more concentrated and will have a higher specific gravity than a specimen passed during the day. A high fluid intake may reduce the specific gravity to below 1.010. In the presence of disease, the specific gravity of a 24-hour specimen may vary from 1.001 to 1.060. Specific gravity is measured with an index refractometer, available as standard equipment at most duty stations. See figure 7-22. The index refracto- meter may be held manually or mounted on a stand like a microscope. The specific gravity of urine is determined by the index of light refraction through solid material. Measure the specific gravity with an index refractometer in the following manner: 1. Hold the index refractometer in one hand. Use the other hand and an applicator stick to place a drop of urine on the glass section beneath the coverglass. 2. Hold the refractometer so that the light reflects on the glass section, and look into the ocular end. Read the number that appears where the light and dark lines meet. This is the specific gravity. Chemical Characteristics Chemical characteristics evaluated during a routine urinalysis include pH, protein, glucose, ketones, and blood. Some laboratories also include tests for bilirubin, urobilinogen, and nitrite, depending on the test strip used. Currently, most medical facilities use the Multistix® and Color Chart, which detects pH, protein, glucose, ketones, blood, bilirubin, and urobilinogen. The Multistix is a specially prepared multitest strip. The strip is simply dipped into the urine specimen and compared to the color values for the various tests on the accompanying chart. The color chart also indicates numerical pH values, which should be reported. Microscopic Examination of Urine Sediment Microscopic examination of urine sediment is usually performed in addition to routine procedures. This examination requires a degree of skill acquired through practice under the immediate supervision of an experienced technician. The specimen used for microscopic examination should be as fresh as possible. Red cells and many formed solids tend to disintegrate upon standing, particularly if the specimen is warm or alkaline. PREPARING SPECIMENS FOR MICRO- SCOPIC EXAMINATION.—To prepare urine specimens for microscopic examination, follow the steps below. 1. Stir the specimen well. 2. Pour 15 ml of urine into a conical centrifuge tube, and centrifuge at 1,500 rpm for 5 minutes. 3. Invert the centrifuge tube and allow all of the excess urine to drain out. Do not shake the tube while it is inverted. Enough urine will remain in the tube to resuspend the sediment. Too much urine will cause dilution of the sediment, making an accurate reading difficult. 4. Resuspend the sediment by tapping the bottom of the tube. 5. With a medicine dropper, mount one drop of the suspension on a slide and cover it with a coverslip. 6. Place the slide under the microscope, and scan with the low-power objective and subdued lighting. 7. Switch to the high-power objective for detailed examination of a minimum of 10 to 15 fields. CLINICALLY SIGNIFICANT FINDINGS.— Leukocytes, erythrocytes, and casts may all be of clinical significance when found in urine sediment. Leukocytes.—Normally, 0 to 3 leukocytes per high-power field will be seen on microscopic examination. More than 3 cells per high-power field probably indicates disease somewhere in the urinary tract. Estimate the number of leukocytes present per high-power field and report it as the “estimated number per high-power field.” Erythrocytes.—Red cells are not usually present in normal urine. If erythrocytes are found, estimate their number per high-power field and report it. Erythrocytes may be differentiated from white cells in several ways:  White cells are larger than red cells. 7-35 HM3f0722 Figure 7-22.—Index refractometer.


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