Page 269 - Cardiac Nursing

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L L L L Laboratory Tests Using Blood
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Susan L. Reed
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resullts to com l tete thee assessment pictture. OOne fof thhe most ffre- b bagg ded at he location where it was used. 3
quently used testing modalities is laboratory testing of blood
specimens. Laboratory analysis comprises approximately 43% of Blood Sample Collection
the data used by health care workers to make clinical decisions. 1
A host of variables can affect interpretation of blood specimen General guidelines for blood sample collection have been devel-
results. Accurate interpretation starts with proper specimen col- oped that help to ensure patient and clinician safety and maximize
lection. The nurse has a key role in maximizing the conditions interpretation of results. The clinician should consider the policies
under which specimens are collected, thereby controlling for as and procedures of his or her organization with regard to blood
many variables as possible. specimen collection, as well as the standards for professional, na-
tional, and international organizations. Control of variability can
be enhanced by use of proper technique during collection and
processing of the specimen.
BLOOD SPECIMEN COLLECTION During specimen collection through venipuncture, the use of
a tourniquet produces changes within the vein. Once a tourniquet
is placed on the arm, veins dilate because of their inability to
Collection of blood specimens is a process that involves three
phases: patient preparation, collection of the blood sample, and drain. Cellular injury and hemolysis can be caused by the pro-
interpretation of results. The nurse plays an important role during longed use of a tourniquet, described as 3 minutes or longer. Un-
these phases. Tests should not have to be repeated due to errors in der these conditions, return of fluid and electrolytes to the vein is
any of these three phases. 2 decreased or prohibited, resulting in a hemoconcentrated speci-
men. In addition, despite decreased circulation of fresh blood to
the tissues, cells continue their metabolic processes, leading to an
increased concentration in metabolic waste products, such as lac-
Patient Preparation
tate. In this more acidic environment, potassium leaks out of cells.
Adequate preparation of patients and their families involves edu- In general, the tourniquet should not be left on more than
2
cation. Frequently, proper specimen collection and interpretation 1 minute. Longer use may be unavoidable during a difficult
requires compliance with instructions about food or fluid restric- venipuncture. In such cases, information about a difficult
tions, taking or withholding medications, and meeting criteria for venipuncture should be noted on the laboratory slip to assist with
proper timing of the blood sample. When the blood sample is interpretation of results.
taken, patients should receive an explanation about what tests are Blood specimens can be contaminated in several ways. Dur-
being drawn, why they have been ordered, and when results will ing collection, contamination may occur from intravenous (IV)
be available. If the sample is being obtained by venipuncture, ar- fluids. Blood draws should not be done on the same arm as an
terial puncture, or vascular port access, preparation of the patient infusion. If the infusion arm cannot be avoided, a tourniquet
includes a reminder about pain during the procedure and the im- may be placed between the IV site and the phlebotomy site.
portance of complying with instructions to maintain a certain Slowing the IV to a keep-open rate (if not contraindicated) for
position. 2 3 to 5 minutes before the draw may help to reduce contamina-
tion of the blood sample. In any event, it should be noted on
the laboratory slip that the sample was obtained under these
Universal Precautions conditions.
Contamination may also be introduced by improper use of
All blood is considered a source of potential infection. Universal blood tubes. Most specimen collection tubes contain some form
precautions, as well as organizational policies and procedures, of anticoagulant. If blood has been mistakenly collected in one
should be followed when collecting and transporting specimens. tube containing anticoagulant, it should never be poured into a
Universal precautions include proper handwashing, the use of different tube. Also, blood entering one tube should never be al-
gloves during phlebotomy (or at any time there is risk of exposure lowed to contaminate remaining blood that will be introduced
to blood or body fluids), complete avoidance of recapping nee- into another tube.
dles, and proper disposal of sharps. When there is the potential Another source of contamination is introduced when routine
that blood or body fluids will splash, protective clothing and samples are drawn from arterial lines, vascular catheters, or
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