1. HEMATOLOGY
INTRODUCTION

2. Composition
The average person circulates about 5 L of blood (1/13
of body weight), of which 3 L is plasma and 2 L is cells.
Plasma fluid derives from the intestines and lymphatic
systems and provides a vehicle for cell movement. The
cells are produced primarily by bone marrow and
account for blood solids. Blood cells are classified as
white cells (leukocytes), red cells (erythrocytes), and
platelets (thrombocytes). White cells are further
categorized as granulocytes, lymphocytes, monocytes,
eosinophils, and basophils.

3. Composition
Before birth, hematopoiesis occurs in the liver. In
midfetal life, the spleen and lymph nodes play a
minor role in cell production. Shortly after birth,
hematopoiesis in the liver ceases, and the bone
marrow is the only site of production of
erythrocytes, granulocytes, and platelets. B
lymphocytes are produced in the marrow and in
the secondary lymphoid organs; T lymphocytes
are produced in the thymus.

4. Collecting Sample
Proper specimen collection presumes correct
technique and accurate timing when necessary.
Most hematology tests use liquid
ethylenediaminetetraacetic acid (EDTA) as an
anticoagulant. Tubes with anticoagulants should
be gently but completely inverted end over end 7
to 10 times after collection. This action ensures
complete mixing of anticoagulants with blood to
prevent clot formation. Even slightly clotted
blood invalidates the test, and the sample must
be redrawn.

5. Capilary puncture
Capillary blood is preferred for a peripheral blood
smear and can also be used for other
hematology studies. Adult capillary blood
samples require a skin puncture, usually of the
fingertip. For children, the tip of the finger is also
often the choice. Infants younger than 1 year of
age and neonates yield the best samples from
the great toe or side of the heel.

6. Capilary puncture -
Procedure
Observe standard precautions. Check for latex allergy. If allergy is present,
do not use latex-containing products.
Obtain capillary blood from fingertips or earlobes (adults) or from the great
toe or heel (infants). Avoid using the lateral aspect of the heel where the
plantar artery is located.
Disinfect puncture site, dry the site, and puncture skin with sterile disposable
lancet, perpendicular to the lines of the patient's fingers, no deeper than 2
mm. If povidone-iodine is used, allow to dry thoroughly.
Wipe away the initial drop of blood. Collect subsequent drops in a microtube
or prepare a smear directly from a drop of blood.
After collection, apply a small amount of pressure briefly to the puncture site
to prevent painful extravasation of blood into the subcutaneous tissues.

7. Dried Blood Spot
In this method, a lancet is used, and the resulting droplets of blood are
collected by blotting them with filter paper directly.
Check the stability of equipment and integrity of supplies when doing a finger
stick. If provided, check the humidity indicator patch on the filter paper card.
If the humidity circle is pink, do not use this filter paper card. The humidity
indicator must be blue to ensure specimen integrity.
After wiping the first drop of blood on the gauze pad, fill and saturate each of
the circles in numerical order by blotting the blood droplet with the filter
paper. Do not touch the patient's skin to the filter paper; only the blood
droplet should come in contact with the filter paper.
If an adult has a cold hand, run warm water over it for approximately 3
minutes. The best flow occurs when the arm is held downward, with the
hand below heart level, making effective use of gravity. If there is a problem
with proper blood flow, milk the finger with gentle pressure to stimulate blood
flow or attempt a second finger stick; do not attempt more than two.
When the blood circles penetrate through to the other side of the filter paper,
the circles are fully saturated.

8. Venipuncture
Venipuncture allows procurement of larger quantities of blood
for testing. Care must be taken to avoid sample hemolysis or
hemoconcentration and to prevent hematoma, vein damage,
infection, and discomfort. Usually, the antecubital veins are
the veins of choice because of ease of access. Blood values
remain constant no matter which venipuncture site is selected,
so long as it is venous and not arterial blood. Sometimes, the
wrist area, forearm, or dorsum of the hand or foot must be
used. Blood values remain consistent for all of these
venipuncture sites.

9. Venipuncture -
procedure
Observe standard precautions (see Appendix A). If latex
allergy is suspected, use latex-free supplies and equipment.
Position and tighten a tourniquet on the upper arm to produce
venous distention (congestion). For elderly persons, a
tourniquet is not always recommended because of possible
rupture of capillaries. Large, distended, and highly visible
veins increase the risk for hematoma.
Ask the patient to close the fist in the designated arm. Do not
ask patient to pump the fist because this may increase plasma
potassium levels by as much as 1 to 2 mEq/L (mmol/L). Select
an accessible vein.

10. Venipuncture -
procedure
Cleanse the puncture site, working in a circular motion from
the center outward, and dry it properly with sterile gauze.
Povidone-iodine must dry thoroughly.
To anchor the vein, draw the skin taut over the vein and press
the thumb below the puncture site. Hold the distal end of the
vein during the puncture to decrease the possibility of rolling
veins.
Puncture the vein according to accepted technique. Usually,
for an adult, anything smaller than a 21-gauge needle might
make blood withdrawal more difficult. A Vacutainer system
syringe or butterfly system may be used.

11. Once the vein has been entered by the collecting needle,
blood will fill the attached vacuum tubes automatically
because of negative pressure within the collection tube.
Remove the tourniquet before removing the needle from the
puncture site or bruising will occur.
Remove needle. Apply pressure and sterile dressing strip to
site.
The preservative or anticoagulant added to the collection tube
depends on the test ordered. In general, most hematology
tests use EDTA anticoagulant. Even slightly clotted blood
invalidates the test, and the sample must be redrawn.

12. Pretest Error
Improper patient identification
Failure to check patient compliance with dietary
restrictions
Failure to calm patient before blood collection
Use of wrong equipment and supplies
Inappropriate method of blood collection

13. Procedure Error
Failure to dry site completely after cleansing with alcohol
Inserting needle with bevel side down
Using too small a needle, causing hemolysis of specimen
Venipuncture in unacceptable area (eg, above an intravenous [IV]
line)
Prolonged tourniquet application
Wrong order of tube draw
Failure to mix blood immediately that is collected in additive-
containing tubes
Pulling back on syringe plunger too forcefully
Failure to release tourniquet before needle withdrawal

14. Posttest Error
Failure to apply pressure immediately to venipuncture site
Vigorous shaking of anticoagulated blood specimens
Forcing blood through a syringe needle into tube
Mislabeling of tubes
Failure to label specimens with infectious disease precautions as
required
Failure to put date, time, and initials on requisition
Slow transport of specimens to laboratory

15. Pretest Patient Care
Instruct patient regarding sampling procedure. Assess for circulation
or bleeding problems and allergy to latex. Verify with the patient any
fasting requirements. Diagnostic blood tests may require certain
dietary restrictions of fasting for 8 to 12 hours before test. Drugs
taken by the patient should be documented because they may affect
results.
Reassure patient that mild discomfort may be felt when the needle is
inserted.
Place the arm in a fully extended position with palmar surface facing
upward (for antecubital access).

16. Pretest Patient Care
If withdrawal of the sample is difficult, warm the extremity with warm
towels or blankets. Allow the extremity to remain in a dependent
position for several minutes before venipuncture. For young children,
warming the draw site should be routine to distend small veins.
Be alert to provide assistance should the patient become
lightheaded or faint.
Prescribed local anesthetic creams may be applied to the area
before venipuncture; allow 60 seconds for light-skinned persons and
120 seconds for dark-skinned persons before performing the
procedure.

17. Posttest Patient Care
Be aware that the patient occasionally becomes dizzy, faint, or
nauseated during the venipuncture. The phlebotomist must be
constantly aware of the patient's condition. If a patient feels faint,
immediately remove the tourniquet and terminate the procedure.
Place the patient in a supine position if possible. If the patient is
sitting, lower the head between the legs and instruct the patient to
breathe deeply. A cool, wet towel may be applied to the forehead
and back of the neck, and, if necessary, ammonia inhalant may be
applied briefly. Watch for signs of shock, such as increased heart
rate and decreased blood pressure. If the patient remains
unconscious, notify a physician immediately.

18. Posttest Patient Care
Prevent hematomas by using proper technique (not sticking the
needle through the vein), releasing the tourniquet before the needle
is withdrawn, applying sufficient pressure over the puncture site, and
maintaining an extended extremity until bleeding stops. If a
hematoma develops, apply a warm compress.
Assess the puncture site for signs and symptoms of infection,
subcutaneous redness, pain, swelling, and tenderness.

19. Arterial Puncture
Arterial blood samples are necessary for arterial
blood gas (ABG) determinations or when it is not
possible to obtain a venous blood sample. Arterial
sticks are usually performed by a physician or a
specially trained nurse or technician because of the
potential risks inherent in this procedure. Samples
are normally collected directly from the radial,
brachial, or femoral arteries. If the patient has an
arterial line in place (most frequently in the radial
artery), samples can be drawn from the line. Be sure
to record the amounts of blood withdrawn because
significant amounts can be removed if frequent
samples are required.

20. Arterial Puncture
ABG determinations are used to assess the status of
oxygenation and ventilation, to evaluate the acid-
base status by measuring the respiratory and
nonrespiratory components, and to monitor
effectiveness of therapy. The ABGs are also used to
monitor critically ill patients, to establish baseline
laboratory values, to detect and treat electrolyte
imbalances, to titrate appropriate oxygen therapy, to
qualify a patient for home oxygen use, and to assess
the patient's status in conjunction with pulmonary
function testing.

21. Contra Indication
Absence of a palpable radial artery pulse
Positive Allen's test result, which shows only one artery
supplying blood to the hand
Negative modified Allen's test result, which indicates
obstruction in the ulnar artery (ie, compromised collateral
circulation)
Cellulitis or infection at the potential site
Presence of arteriovenous fistula or shunt
Severe thrombocytopenia (platelet count 20,000/mm3)
Prolonged prothrombin time or partial thromboplastin time
(>1.5 times the control is a relative contraindication)

22. Intratest patient care
Perform a modified Allen's test by encircling the wrist area and
using pressure to obliterate the radial and ulnar pulses. Watch
for the hand to blanch, and then release pressure only over
the ulnar artery. If the result is positive, flushing of the hand is
immediately noticed, indicating circulation to the hand is
adequate. The radial artery can then be used for arterial
puncture. If collateral circulation from the ulnar artery is
inadequate (ie, negative test result) and flushing of the hand is
absent or slow, then another site must be chosen. An
abnormal Allen's test result may be caused by a thrombus, an
arterial spasm, or a systemic problem such as shock or poor
cardiac output.

23. Intratest patient care
Elevate the wrist area by placing a small pillow or rolled towel
under the dorsal wrist area. With the patient's palm facing
upward, ask the patient to extend the fingers downward, which
flexes the wrist and positions the radial artery closer to the
surface.
Palpate for the artery, and maneuver the patient's hand back
and forth until a satisfactory pulse is felt.
Swab the area liberally with an antiseptic agent such as
Chloraprep.

24. Intratest patient care
Prepare a 20- or 21-gauge needle on a preheparinized, self-
filling syringe; puncture the artery; and collect a 3- to 5-mL
sample. The arterial pressure pushes the plunger out as the
syringe fills with blood. (Venous blood does not have enough
pressure to fill the syringe without drawing back on the
plunger.) Air bubbles in the blood sample must be expelled as
quickly as possible because residual air alters ABG values.
The syringe should then be capped and gently rotated to mix
heparin with the blood.

25. Intratest patient care
When the draw is completed, withdraw the needle, and place
a 4- ร— 4-inch absorbent bandage over the puncture site. Do
not recap needles; if necessary, use the one-handed
mechanical, recapping, or scoop technique or commercially
available needles (eg, B-D Safety-Glide [Franklin Lakes, NJ]
or Sims Portex Pro-Vent [Keene, NH]). Maintain firm finger
pressure over the site for a minimum of 5 minutes or until
there is no active bleeding evident. After the bleeding stops,
apply a firm pressure dressing but do not encircle the entire
limb, which can restrict circulation. Leave this dressing in
place for at least 24 hours. Instruct the patient to report any
signs of bleeding from the site promptly and apply finger
pressure if necessary.

26. Posttest patient care
Frequently monitor the puncture site and dressing for arterial
bleeding for several hours. The patient should not use the
extremity for any vigorous activity for at least 24 hours.
Monitor the patient's vital signs and mental function to
determine adequacy of tissue oxygenation and perfusion.
The arterial puncture site must have a pressure dressing
applied and should be frequently assessed for bleeding for
several hours. Instruct the patient to report any bleeding from
the site and to apply direct pressure to the site if necessary.

27. Posttest patient care
For patients requiring frequent arterial monitoring, an
indwelling arterial catheter (line) may be inserted. Follow
agency protocols for obtaining arterial line blood samples. The
procedure varies for neonate, pediatric, and adult patients.
Label all specimens appropriately, and document pertinent
information in the health care record.