CLINICAL LAB SCIENEC

CHAPTER 14: CLINICAL CHEMISTRY 367
2. Specimens containing an anticoagulant must be mixed properly to avoid
clots.
3. Hemolysis (the breakdown of red blood cells) may release interfering
substances.
4. Lipema, a high level of fatty materials in the serum or plasma, must be noted for
proper interpretation of results, or the specimen should be recollected.
5. Specimens must not leak contents onto the outer portion of the tube. Certain
specimens may require that they be sealed in leak-proof containers.
6. Timely delivery to the laboratory and proper storage of specimens that will
not be analyzed until later is of great importance.
7. Short draws are those in which the tube was not completely
filled and therefore contains less volume than designed for a
given amount of anticoagulant. This will result in an improper
dilution ratio and will affect results.
8. Patients being administered IV solutions or who have other
implanted devices will require care in the collection of blood.
Blood should never be drawn from above an active IV site.
Many safety devices are provided for handling samples,
as this process involves the greatest risk when performing clinical chemistry
exams. Most of the chemicals utilized in chemistry procedures are quite
safe today. However, in the past, many toxic chemicals were used that were
carcinogenic (cancer-causing) or could cause serious tissue damage, such as
caustics that might “burn” the skin or the mucous membranes. Uncapping
tubes (removing the specialized plastic and rubber tops) presents an opportunity
for exposure to biohazards. By using a safety shield, this danger is
minimized. Some instruments pierce the cap of the tube and aspirate the
sample without the medical laboratory worker being required to uncap the
tube.
Other considerations in the chemistry laboratory are the collection of timed
specimens that either are to be collected at a specific time of day or in a timed
sequence to determine a patient’s response to medication or food. Fasting
specimens are required for some procedures to obtain a baseline or to avoid
lipemia (fats in the blood that cause turbidity). Other reasons for requiring
samples from fasting patients are to avoid foods containing certain chemicals
that may elevate or decrease the values of some laboratory tests. An example
of this would be testing for blood glucose level, which may be elevated if a
blood sample is taken within an hour of a meal that contains carbohydrates
and glucose. But even if due diligence and care are exercised for preanalytical
factors and the condition of supplies and operations of equipment are
adequate, random errors (those whose cause is undetermined) will occur on
a statistical basis. Random errors affect precision (reproducibility) and may
occur due to a variety of factors, including technique and environmental
conditions under which the procedures are performed. As one might recall
from the chapter on quality control, roughly 5% of results will be outside an
acceptable range.
Critical Reminder
The factors listed here are preanalytical
components of performing a laboratory
procedure. Errors in any of these steps
are capable of providing erroneous results
that may harm a patient, hindering a
proper diagnosis.
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