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Blood
Hematology: Is defined as the study of blood.
Everybody is familiar with the sight of blood - the red
fluid that oozes out of your body when you've
sustained a cut or a deep injury, which is slightly
denser and approximately 3-4 times more viscous than
water.
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Blood volume:
Blood volume is variable, but tends to be about 8% of
body weight. Factors such as body size, amount of
adipose tissue, and electrolyte concentrations all affect
volume. The average adult has about 5 liters of blood.
Blood composition
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Blood consists of cells which are suspended in a liquid.
The components of blood can be separated by filtration,
however, the most common method of separating blood
is to centrifuge (spin) it.
Three layers are visible in centrifuged blood.
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The straw-colored liquid portion, called plasma, forms at the
top (~55%).
A thin cream-colored layer, called the buffy coat, forms
below the plasma. The buffy coat consists of white blood cells
and platelets.
The red blood cells form the heavy bottom portion of
the separated mixture (~45%).
Blood composition
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The plasma:
Plasma is a straw colored liquid, most of which is
water. It makes up 55% of the blood and serves as a
transport medium for blood cells and platelets.
By far the greatest constituent of plasma is water,
which accounts approximately 90% of the total
volume.
Other constituents (10%) fall into the following main
categories:
Ions (Na+, CL-, etc)
Plasma proteins (albumins, globulins, fibrinogen, etc)
Dissolved gases (O2, CO2).
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Circulating Nutrients (glucose, amino acids, etc)
Circulating Tissue products (urea, creatinine, lactate,
etc)
Circulating Hormones (insulin, adrenaline, etc)
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The water in the plasma is an important solvent for
ions such as Na+, CL-, K+, etc. It also dissolves
nutrients like simple sugar, lipids, amino acids and
vitamins. Sometimes, it would help transport
enzymes and hormones, but that depends on the
activities of the body.
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Serum: Plasma differs slightly from what is termed
serum, which is generally taken to mean the fluid part
of the blood which remains after the blood has
coagulated (clotted).
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The red blood cells:
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The red blood cells form a major part of the blood.
These are the familiar discotic shaped cells which
make up 99% of the cells in the blood.
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They are the principal carriers of the red colored
hemoglobin molecules.
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Hemoglobin is an iron containing protein and binds
about 97% of all oxygen in the body; hence, the most
principled function of red blood cells is to carry
oxygen gas around the body. Although they do carry a
little carbon dioxide sometimes, most of this unwanted
gas is transported by the plasma
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The white blood cells:
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The white blood (leukocytes) cells are a vital source
of defense against external organisms.
White blood cells also serve as 'sanitary engineers'
cleaning up dead cells and tissue debris that would
otherwise accumulate to and lead to problems.
There are five classes of leukocytes: Neutrophil,
Eosinophil, Basophil, Monocyte and Lymphocytes.
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The platelets:
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These are not true cells but fragments of cytoplasm
from certain bone marrow cells. They play a part in
the clotting of blood.
Role of plasma and platelets in clotting
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If damage occurs to a blood vessel, circulating platelets
immediately get trapped at the injury site. On
accumulating the platelets 'plug' the leak in the vessel
providing a first step in damage control.
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This mechanism is supplemented by 'blood coagulation',
or clotting, which is the most important means of
defense against bleeding.
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As mentioned plasma contains several dissolved
proteins. Fibrinogen is a rod shaped soluble protein
which in the presence of a catalyst thrombin gets
converted to an insoluble protein fibrin.
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The combined action of the platelets and 'fibrin web' is
sufficient to prevent a dangerous loss of blood.
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In cases where the formation of fibrin and hence
formation of a clot is impaired due to some reason (e.g.
a genetic disorder as in hemophilia) a person is at great
risk of bleeding to death.
Blood Cells
Venipuncture
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Venipuncture or phlebotomy: is a procedure done
to have an access to a vein (Blood collection, IV).
There are three veins most commonly used in
venipuncture, or phlebotomy:
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The cephalic
The median cubital
The basilic veins
These three veins are found in the
antecubital area.
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Common Sites for
Venipuncture
The median cubital vein is the preferred vein for
phlebotomy because:
• It is usually larger than the other veins.
• Best anchored vein (More stationary(.
 Median Cubital – First Choice
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Well anchored vein, usually large and prominent.
Very few problems. Offering the best chance for a close to painless puncture,
as there are few nerve endings close to this vein.
Cephalic Vein – Second Choice: The cephalic vein may lie
close to the surface.
Basilic Vein – Third Choice
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In many patients this vein may not be well anchored and will roll, making it
difficult to access with the needle.
Additionally, this area is often more sensitive, thus a stick is slightly more
painful for the patient
Hand Veins
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At times, none of the veins of the antecubital fossa will be felt or
not be able to be used due to intravenous placement or injury,
hand veins may be used.
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Veins of the hand and wrist are usually close to the surface, but
they are prone to movement and rolling.
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Using these veins tends to be more painful for the patient, since
there are nerves running through the hand as well.
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If using these veins, it is important to anchor the vein with your
hand, holding it in place, when you are drawing the blood.
Venipuncture, why?
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Intravenous therapy
Venous blood sample
Treatment of certain diseases (hemochromatosis)
Parenteral nutrition
Perform the Venipuncture process including
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Proper patient identification procedures.
Proper equipment selection and use.
Proper labeling procedures and completion
of laboratory requisitions.
Preferred venous access sites, and factors to
consider in site selection, and ability to
differentiate between the feel of a vein,
tendon and artery.
Patient care following completion of
venipucture.
Safety and infection control procedures.
Venipuncture Procedure
1. Identify the patient.
2. Check the requisition form for requested tests, patient
information, and any special requirements.
3. Select a suitable site for venipuncture.
4. Prepare the equipment, the patient and the puncture site.
5. Perform the venipucture.
6. Collect the sample in the appropriate container.
7. Recognize complications associated with the phlebotomy
procedure.
8. Assess the need for sample recollection and/or rejection.
9. Label the collection tubes at the bedside or drawing area.
10. Promptly send the specimens with the requisition to the
laboratory
Order form / Requisition
Type of fluid
Labeling the Sample
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Patient's name, first and middle.
Patient's ID number.
NOTE: Both of the above MUST match the same
on the requisition form.
Date, time and initials of the phlebotomist must be
on the label of EACH tube.
Equipment
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Needles (Smaller gauge numbers indicate larger
outer diameters.)
Syringes
Cotton
Alcohol
Tourniquet
Collection tubes
Adhesive bandages
Gloves
Sharp box
Needle and Syringes Components
Butterfly Needle
Procedural Issues
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Proper patient identification is MANDATORY match
with that on the request form
Ask for a full name
An outpatient must provide identification other than
the verbal statement of a name.
Speak with the patient during the process
Venipucture Site Selection
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Median cubital then cephalic veins of the arm are used
most frequently
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Avoid
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Extensive scars from burns and surgery
Hematom.
Intravenous therapy (IV) / blood transfusions
Turn off the IV for at least 2 minutes before
venipuncture.
Apply the tourniquet below the IV site. Select a vein
other than the one with the IV.
Perform the venipuncture. Draw 5 ml of blood and
discard before drawing the specimen tubes for testing.
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Procedure for Vein Selection
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Palpate and trace the path of veins with the index
finger. Arteries pulsate, are most elastic, and have a
thick wall.
If superficial veins are not readily apparent, you can
force blood into the vein by massaging the arm from
wrist to elbow, tap the site with index and second
finger, apply a warm, damp washcloth to the site for 5
Median basalic
minutes.
Median Cephalic
Cephalic vein
Performance of a Venipucture
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Position the patient. The patient should either sit in a chair, lie
down or sit up in bed.
Apply the tourniquet 3-4 inches above the selected puncture
site. Do not place too tightly or leave on more than 2 minutes.
The patient should make a fist without pumping the hand.
Select the venipuncture site.
Prepare the patient's arm using an alcohol prep.
Cleanse in a circular fashion, beginning at the site and working
outward.
Allow to air dry.
Grasp the patient's arm firmly using your thumb to draw the
skin taut and anchor the vein. The needle should form a 15 to
30 degree angle with the surface of the arm. Swiftly insert the
needle through the skin and into the lumen of the vein. Avoid
trauma and excessive probing.
The needle bevel up
Venipuncture Procedure after Tracing the Vein
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When the blood is drawn is , remove the tourniquet.
Remove the needle from the patient's arm using a
swift backward motion.
Press down on the gauze once the needle is out of the
arm, applying adequate pressure to avoid formation
of a hematoma.
Dispose of contaminated materials/supplies in
designated containers.
Mix and label all appropriate tubes at the patient
bedside.
Deliver specimens promptly to the laboratory.
Blood won’tflow
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If you do not see blood flow, the tip of the needle:
May not yet be within the vein.
May have already passed through the vein.
May have missed the vein entirely.
May be pushed up against the inside wall of the vein.
If An Incomplete Collection Or No Blood Is Obtained
Move forward
Adjust the angle
Move backward
Withdraw and pressure for
5 min
A hematoma forms under the
skin adjacent to the puncture
site - release the tourniquet
immediately and withdraw the
needle. Apply firm pressure.
Loosen the tourniquet
Performance of a fingerstick
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The best locations for fingersticks are the 3rd (middle)
and 4th (ring) fingers of the non-dominant hand.
Do not use the tip of the finger or the center of the
finger.
Avoid the side of the finger where there is less soft
tissue, where vessels and nerves are located, and
where the bone is closer to the surface.
The 2nd (index) finger tends to have thicker, callused
skin.
The fifth finger tends to have less soft tissue overlying
the bone.
Avoid puncturing a finger that is cold or cyanotic,
swollen, scarred, or covered with a rash.
• Sterile
• Single-use
• Different lengths
Lancets
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Using a sterile lancet, make a skin puncture just off
the center of the finger pad.
The puncture should be made perpendicular to the
ridges of the fingerprint so that the drop of blood does
not run down the ridges.
Wipe away the first drop of blood, which tends to
contain excess tissue fluid.
Collect drops of blood into the collection device by
gently massaging the finger.
Avoid excessive pressure that may squeeze tissue
fluid into the drop of blood.
Finger stick
Blood Collection on Babies
Prewarming the infant's heel is important.
• Clean the site to be punctured with an alcohol sponge.
Dry the cleaned area with a dry cotton sponge.
• Hold the baby's foot firmly to avoid sudden
movement.
• Do not use the central portion of the heel because
you might injure the underlying bone, which is close to
the skin surface.
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• Do not use a previous puncture site.
• Make the cut across the heel print lines so that a drop
of blood can well up and not run down along the
lines.
• The recommended location for blood collection on a newborn
baby or infant is the heel.
• The diagram below indicates in green the proper area to use
for heel punctures for blood collection:
To prevent a hematoma
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Puncture only the uppermost wall of the vein.
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Remove the tourniquet before removing the needle.
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Use the major superficial veins.
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Make sure the needle fully penetrates the upper most
wall of the vein. (Partial penetration may allow blood
to leak into the soft tissue surrounding the vein by
way of the needle bevel).
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Apply pressure to the venipucture site.
To prevent hemolysis
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Mix tubes with anticoagulant additives gently 5-10
times.
Avoid drawing blood from a hematoma.
Avoid drawing the plunger back too forcefully, if
using a needle and syringe.
Make sure the venipucture site is dry.
Avoid a probing, traumatic venipuncture.
Hemoconcentration
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An increased concentration of larger molecules and
formed elements in the blood may be due to several
factors:
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Prolonged tourniquet application (no more than 2 minutes).
Massaging, squeezing, or probing a site.
Long-term IV therapy.
Anticoagulants
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The blood is withdrawn from the patient, it is mixed
with an anticoagulant to prevent coagulation.
The three most commonly used anticoagulants in the
hematology laboratory are discussed below:
1- EDTA:
• Is generally available as the sodium, dipotassium or
tripotassium salt of ethylene diamine tetra acetic acid. It
is used in concentration of (1.5±.25).
• EDTA prevents coagulation by binding the calcium in
the blood (calcium is required for blood coagulation).
Excessive concentration of EDTA cause:
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Shrinkage of the red blood cells leading to decreased
hematocrit increased MCHC, falsely low ESR.
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Degenerative changes in the white cells and the
platelets will swill and break up causing a falsely
increased in platelet counts.
2- Sodium citrate:
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Used for coagulation studies in a concentration of 1
part 0.109M sodium citrate (tri sodium citrate
dehydrate) to 9 part whole blood.
Sodium citrate prevents coagulation by binding the
calcium of the blood in a soluble complex.
3- Heparin:
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May be used in concentration of 15 to 30 units/ml of
whole blood. its may cause clumping of platelets and
white cells.
Coagulation is prevented by interaction with anti
thrombin III and subsequent inhibition of thrombin.
Fainting; what to do?
• Rarely, patients will faint during venipuncture.
• It is therefore important that patients are properly seated
or lying in such a way during venipuncture so that if they do
faint, they won’t hurt themselves.
• self-limited
Fainting; what to do?
• Gently remove the tourniquet and needle from the patients
arm, apply gauze and pressure to the skin puncture site.
• Call for help.
• If the patient is seated, place him on his back, with his hips
flexed to help blood return to the brain.
• A cold compress on the back of the neck may help to revive
the patient more quickly.