CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
force components of the blood to assume certain levels based on density of
the constituents), the specimen must be allowed to clot undisturbed for up to
30 minutes. Centrifugation before a complete clot is achieved will result in a
fibrin clot that requires removal before use of the specimen. Small fibrin clots
may cause blockages in the small lines that carry the specimen in an automated
instrument. Separation of serum and plasma from the cells should be
performed immediately. This avoids consumption of some materials from
the liquid portion by the blood cells and slight mixing of red cells with the
plasma or serum, resulting in erroneous results.
4. Contamination by bacteria is a common occurrence that will render results
invalid for treating patients. Often the serum or plasma will become cloudy if
contaminated by bacteria, since some bacteria multiply rapidly and may completely
cloud the sample within a few hours. These bacteria, depending on
their species, use materials from the blood for their own metabolism, thereby
lowering the levels of certain components, particularly glucose. Byproducts
of bacterial metabolism may also cause falsely elevated or lowered results for
certain tests.
5. Chemical contamination may occur for several reasons. The tubes themselves
may have somehow become contaminated, or if samples are transferred to
other tubes, contamination may occur during the transfer through use of
unclean syringes or pipette tips. Chemical contamination of test reagents
will create the same problem results as that of specimen contamination.
The phlebotomist and the laboratory professional must become familiar with
the wide variety of vacuum collection tubes. Tubes intended for similar purposes
may vary in appearance depending on their manufacturer. Figure 11-16 shows a
representative sample of the variety of collection tubes available.
FIGURE 11-16 A sampling of the many types of blood collection tubes available. Note the barrier substances in three
of the tubes.
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