CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
In the Lab
3. Pour the urine sample into a disposable 12-mL centrifuge tube (Figure 12-13).
a. If less than 1 mL urine is collected, do not centrifuge the sample.
b. If the microscopic exam is performed on uncentrifuged urine, note it on the
report.
4. Centrifuge tubes for 5 minutes at 400 RCF*.
5. Pour off the supernatant (Figure 12-11A) and resuspend the sediment with urine
remaining in the centrifuge tube designed for concentrating urine sediment.
Approximately 0.8 mL urine supernatant and 0.1 mL of urine sediment will remain
in the bottom of the tube. If graduated tubes or pipetters are used, follow the
directions provided by the manufacturer.
The use of a stain for the urinary sediment is optional. After the supernatant is
poured off, a drop of stain is added to the remaining 0.8 mL of concentrated sample,
and it is mixed by aspirating and emptying the pipette bulb repeatedly several
times.
6. Place a drop of the resuspended urine sediment onto a glass slide and place
a cover slip over the suspension. Or, follow the instructions for using an engineered
system (e.g., Kova) for examining urinary sediment (see
Figure 12-11C).
7. Place the sample on the stage of the microscope (Figure 12-11D and Figure 12-14)
8. Adjust the microscope condenser down and close the diaphragm so that light is
subdued to provide better visualization of sometimes colorless constituents.
9. Scan at least 10 fields using the low-power objective and subdued light. (Hyaline
casts and other partially transparent solid elements may be obscured by excessively
bright light.) Count the number of casts seen per low-power field (LPF)
and record the average number casts/LPF in the Procedure Report Form.
10. Scan at least 10 fields using the high-power objective. Count and record the average
range of red blood cells (RBCs) per high-power field (HPF). If more than
100 RBCs are present, record 100/HPF in the Procedure Report Form.
11. If the field is obscured by more than 100 RBCs/HPF, add a drop of 2% acetic acid
to 2 drops of urine sediment to lyse the RBCs so that other cells and elements
may be counted. RBCs may be confused with yeast, fat droplets, and degenerated
epithelial cells.
12. Observe and note RBC morphology. If the RBCs were lysed in Step #11, it may
be advisable to dilute a small portion of the unlysed sample before performing a
microscopic evaluation of the morphology of the RBCs.
a. Normal, unstained RBCs in wet preparations sometimes appear as pale
yellow-orange discs. They vary in size, but are usually about 8 microns in
diameter.
Note: *RCF is the acronym for relative centrifugal force and is a method of comparing the force generated by various
centrifuges on the basis of the speeds of rotation and distances from the center of rotation. For clinical laboratory
procedures, the RCF required is quite low.
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