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REVIEW OF BLOOD COLLECTION EQUIPMENT
OBJECTIVES:
INTRODUCTION:
Phlebotomy is the practice of drawing blood. The word phlebotomy is derived
from Greek: phlebo- means vein and –tomy means to make an incision.
Some authorities believe phlebotomy dates back to the last period of the Stone
Age when crude tools were used to puncture vessels to allow excess blood to
drain out of the body. There is evidence of bloodletting in Egypt around 1400
B.C. in a painting in a tomb showing the application of a leech to a patient.
Even in the Middle Ages barber surgeons flourished by performing bloodletting,
wound surgery, cupping, leeching, shaving, extraction of teeth and administering
of enemas. The familiar stripes on the barber pole symbolized red for blood
and white for bandages.
Early phlebotomy equipment consisted basically of a bleeding bowl, leech jar,
cupping glass, evacuating pump and lancets called fleams.
During the 17th and 18th centuries, phlebotomy was considered a major therapeutic
treatment process and anyone willing to claim medical training could perform
phlebotomy. The practice of phlebotomy continues today, however, principles
and methods have dramatically improved. Phlebotomy now has certain characteristics
that balance knowledge and theory with practical expertise.
Today the main purpose of phlebotomy is to obtain blood for diagnostic testing,
to remove blood for transfusion purposes, and in therapy of patients with polycythemia
(a disease involving overproduction of red blood cells) or hemochromatosis (a
rare disease characterized by excess iron deposits throughout the body). It
involves highly developed and rigorously tested procedures and equipment to
ensure the safety and comfort of the patient and the integrity of the sample
collected.
Phlebotomy skills and responsibilities are performed in a variety of healthcare
settings ranging from hospital care units to home health settings. Furthermore,
phlebotomy practice is more widely performed by all types of health care professionals
including nurses, respiratory therapists, emergency medical technicians (EMT’s),
and clinical laboratory professionals.
This continuing education unit will review the primary duties of the phlebotomist
and the equipment necessary to collect a sample from an adult patient, using
safety techniques.
GENERAL BLOOD COLLECTION EQUIPMENT:
The standard phlebotomy cart or tray contains the following blood collection
equipment: gloves, antiseptics and disinfectants, gauze pads or cotton balls,
bandages, evacuated blood collection tubes, needles and sharps disposal containers, safety goggles
(when needed) arterial puncture equipment, skin puncture equipment, venipuncture
equipment, a tourniquet and pen. A vein locating device is an optional but useful
tool in locating veins that are difficult to see or feel. One such transilluminator
device, called the Venoscope, shines a bright light through the patient’s skin.
When it is positioned properly, veins are visible as dark lines within the tissue.
This works especially well for finding veins in the hand and foot.
The most commonly used tourniquet is a flat strip of stretchable latex, 15-18
inches long. Latex does not readily support bacterial growth and is easily wiped
clean with disinfectant, if soiled. A blood pressure cuff may be used in place
of a tourniquet for those familiar with its operation. Other available types
of tourniquets are Velcro-closure and buckle-closure tourniquets. One disadvantage
to these types of tourniquets is that they are not easily cleaned if contaminated,
and they are not useful for obese or very thin arms. Disposable, OSHA approved,
nonlatex tourniquets are also available and may be a good option to reduce the
risk of latex sensitivity reactions.
Latex gloves have proved effective in preventing transmission of infectious
diseases to Health Care workers. However, exposures to latex can result in an
allergic reaction in some individuals. Since reports of allergic reactions to
latex have increased among health care workers in recent years, the National
Institute for Occupational Safety and Health has developed steps to protect
oneself from latex exposure. Some suggestions are to use powder-free gloves
with reduced protein content, try other brand of gloves or wear cotton gloves
underneath the latex gloves. Many facilities have gone over entirely to nitrile gloves which do not contain
powder and come in a variety of colors.
EVACUATED (VACUUM) TUBE SYSTEMS:
Evacuated tubes can be used with both the evacuated tube system and with the
syringe method of obtaining blood specimens. It is the most direct and efficient
method for obtaining a blood specimen. With the evacuated tube system, the blood
is collected directly into the tube during the venipuncture procedure. With
the syringe method, the blood from the syringe must be transferred into the
tubes after collection.
The evacuated tube system requires three components: the evacuated sample tube,
the double-pointed needle and a special plastic holder. One end of the double-pointed
needle enters the vein and the other end pierces the top of the tube, and the
vacuum aspirates the blood. The evacuated tubes fill with blood automatically
because of a vacuum that exists inside the tube. The amount of vacuum is pre-measured
so that the tube will draw a precise amount of blood. A tube that has lost its
vacuum will not fill with blood. Although the tube vacuum is guaranteed by the
manufacturer until the expiration date printed on the label, premature loss
of vacuum can occur from opening the tube, dropping the tube, advancing the
tube too far onto the needle holder prior to venipuncture, or pulling the needle
bevel partially out of the skin during venipuncture.
This convenient system eliminates the need for syringes in many cases and consists
of disposable needles and tubes. Evacuated tubes are made of glass or plastic
and come in various sizes ranging from 2 to 15 mL. The size is selected according
to the age of the patient, the amount of blood needed for the test, and the
size and condition of the patient’s vein. Some evacuated tubes are coated on
the inside with silicon to help prevent destruction of red blood cells, keep
the blood from sticking to the sides of the tube or prevent activation of clotting
factors. Evacuated tubes may or may not contain additives. Blood collected in
tubes without additives will clot and yield serum on centrifugation. Tubes that
contain additives may or may not clot, depending on the type of additive they
contain. Many tubes are specifically designed to be used directly with chemistry,
hematology or microbiology instrumentation. In these cases, the tube of blood
is identified by its bar code label and is pierced by the instrument probe.
Some sample is aspirated into the instrument for analysis. Use of this type
of closed system minimizes laboratory personnel’s risk of exposure to blood.
Evacuated tubes can also be used for transferring blood from a syringe into
the tubes. The syringe needle is simply pushed through the top of the tube,
and the blood is automatically pulled into the tube system because of the vacuum.
The vacuum tube should be placed in a rack before pushing the needle into the
tube top. In order to prevent damage to the cellular components which cause
hemolysis or cause forceful expulsion of blood, a safety syringe shielded transfer
device needs to be used to avoid the possible exposure to the patient’s blood.
Several manufacturers have developed needle removal systems with safety in mind.
One safety needle holder allows the user to release the needle into the needle
container without unscrewing it from the holder. This prevents injuries associated
with needle disposal and allows the holder to be reused. Other holders have
protective devices that cover the needle after use. Most are designed to be
used with special disposal equipment that accommodates the particular features
of the adaptor.
Whether you choose the evacuated tube system or the syringe system for collecting
blood, the safety holders (preferably disposable) and shields are mandatory
parts of your technique.
ANTICOAGULANTS:
Traditionally, in most clinical laboratories, serum, plasma, or whole blood
has been used to perform the various assays. More recently heparinized whole
blood has become the specimen of choice for the latest clinical laboratory instruments
used in stat and urgent situations. Using whole blood as a specimen decreases
the time involved in acquiring test results because it is not necessary to wait
for the specimen to clot before centrifuging the sample, which adds another
5-10 minutes to turn-around time. Whole blood is achieved in a sample by drawing
the blood in a tube with an anticoagulant.
An anticoagulant is a substance that prevents blood from coagulating or clotting.
There are two methods to prevent coagulation 1) chelating (binding) or precipitating
calcium and making it unavailable for the coagulation process or 2) inhibiting
formation of the thrombin needed to convert fibrinogen to fibrin. In addition
to using the correct anticoagulant for a specific laboratory assay, using the
correct amount of anticoagulant in the blood specimen is important. If an insufficient
amount of blood is collected in a tube with anticoagulant, the laboratory test
results may be erroneous because of an incorrect blood-to-anticoagulant ratio.
The blood collection vacuum tubes have been designed for a certain amount of
blood to be drawn into the tube by vacuum according to the amount of pre-filled
anticoagulant in the tube.
The most common anticoagulants include:
There are a series of other agents used in conjunction with or without the
anticoagulant.
They are antiglycolytic agents, clot activators, and thixotropic gel separators.
The antiglycolytic agent is a substance that inhibits glycolysis or metabolism
of glucose by the cells of the blood. The most common ones are sodium fluoride
and lithium iodoacetate. A clot activator is a substance that initiates or enhances
coagulation and provides increased surface for platelet activation such as glass
or silica particles. Thixotropic gel separator is an inert (non-reacting) synthetic
substance that forms a physical barrier between the cells and the serum or plasma.
This physical separation prevents the cells from continuing to metabolize substances,
like glucose, in the serum or plasma. Gel separator serum tubes have yellow
plastic or mottled red/gray rubber stoppers (aka: tiger topped or SST) and gel
separator plasma tubes have light green plastic or mottled gray/green rubber
stoppers (PST).
CLEANING AND PROTECTING THE PUNCTURE SITE:
Antiseptics and disinfectants are used to reduce the risk of infection. Antiseptic
refers to an agent used to clean living tissue. Disinfectant refers to an agent
used to clean a surface other than living tissue. Antiseptics are used to clean
the patient’s skin before routine venipuncture collection in order to prevent
contamination by normal skin bacteria. The most commonly used antiseptic is
70% isopropyl alcohol. Isopropyl alcohol (rubbing alcohol) is bacteriostatic,
which means it inhibits growth of bacteria but does not kill them. Prepackaged
alcohol “prep pads” are the most commonly used product.
Stronger antiseptics are used when more stringent infection control is needed,
such as for blood cultures or arterial punctures. Betadine (povidone-iodine
solution) is commonly used for these cases. For patients who are allergic to
iodine, chlorhexidine gluconate or benzalkonium chloride (Zephiran Chloride)
is available. These antiseptics are harsher to the skin so they should be washed
off with alcohol after collection. Bleach is too toxic to use on human skin
but is a good disinfectant for cleaning equipment.
After drawing blood, the phlebotomist takes care to stop the bleeding by applying
pressure to the puncture site. This is done by using a 2- by 2-inch gauze pad
folded into quarters. When the bleeding stops, gauze is taped over the puncture
site with paper tape or an adhesive bandage.
Cotton balls are no longer recommended by NCCLS (National Committee for Clinical
Laboratory Standards) because the cotton sticks to the platelet plug and may
pull it out when removed, thus starting the bleeding process again.
NEEDLES:
There are a variety of needles used for phlebotomy. The gauge of the needle
indicates the size of the needle and refers to the diameter of the lumen (internal
space) or “bore” of the needle. The diameter of the needle and the gauge number
have an inverse or opposite relationship. The larger the gauge number, the smaller
the actual diameter of the needle. Gauge selection depends upon the size and
condition of the patient’s vein.
Multiple-sample needles are used with vacuum collection tubes and the holder
to allow for multiple tube changes without blood leakage within the plastic
holder. This needle has a plastic cover over the tube-top puncturing portion
of the needle. This cover creates a leakage barrier. Evacuated tube system needles
come in two lengths: 1 inch and 1 ½ inches. Length selection depends
primarily upon user preference and the depth of the vein. Evacuated tube system
needles are available in sizes 20 to 22 gauge, with the 21 gauge most commonly
used for routine venipuncture. The Single-sample needle is used for collecting
blood with a syringe when a patient presents with difficult veins. These needles
come pre-packaged in a wide range of gauges and in 1 inch and 1 ½ inch
lengths.
The butterfly needle, also referred to as a winged infusion set of blood collection
set, is the most commonly used intravenous device. It is a stainless steel beveled
needle and tube with attached plastic wings on one end and a Luer fitting attached
to the other end. Although they generally come with attachments that allow them
to be used with syringes, a special multiple sample Luer adaptor allows them
to be used with evacuated tube systems. The most common butterfly needle sizes
are 21, 23, and 25 gauges. The butterfly needle is used in the collection of
blood from patients who are difficult to stick by conventional methods. These
would include geriatric patients, cancer patients and for exclusive use in pediatrics.
They are not used routinely as the small bore needle can cause hemolysis.
ORDER OF DRAW:
Remembering which tests are affected by the various additives can be difficult.
The order of draw eliminates confusion by presenting a sequence of collection
that results in the least amount of carryover from one sample tube to the other.
Carryover can also be minimized by making certain that specimen tubes fill from
the bottom up during collection and that the contents of the tube do not come
in contact with the stopper puncturing needle during the draw. EDTA causes more
carryover problems than any other additive. Tests affected by EDTA contamination
are Calcium, PTT, Potassium, Prothrombin Time, Serum Iron and Sodium. Heparin
contamination affects the activated clotting time, Partial Thromboplastin Time
(PTT) and Prothrombin Time (PT). Potassium oxalate contamination affects the
Potassium result and red blood cell morphology.
The order of draw for the evacuated tube system is as follows:
The order of draw for the syringe system was designed to deliver blood first for those tests most affected by microclot formation. This method assumes that the blood entering the syringe last is the freshest and that this blood will be the first blood out of the syringe during the transfer process. Because the clotting process is activated the minute the blood starts to fill the syringe, it is important to transfer the blood quickly and to fill anticoagulant tubes before the serum tubes.
The order of draw for the syringe system order of draw is as follows:
SAFETY & NEEDLE DISPOSAL SYSTEM:
We have discussed safety shields for needles, and safety needle holders. There
are also needle disposal systems available for needle removal with safety in
mind. Needles and syringes must be discarded in puncture resistant plastic containers,
which reduce the possibility of needle sticks for the phlebotomist. There are
several sizes of needle-disposal containers for use in carts, phlebotomy trays,
at the bedside, in surgery or home health situation. Make sure that you are
properly disposing of your needles after each patient draw.
CONCLUSION:
This exercise is a review of blood collection equipment and procedures necessary
for the collection of blood. Emphasis is placed on anticoagulated and non-additive
blood collection tubes, the use of color coding on tubes, the use of gloves,
syringes, needles, and other supplies needed for safe and effective collection
procedure. Anticoagulant types and mechanisms of action of anticoagulants, as
well as order of draw of various tubes are also discussed.
REFERENCES:
Review Questions - Review of Blood Collection - Course #056-954
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