LESSON 3
Section I. COLLECTION OF BLOOD SPECIMENS
3-1.
INTRODUCTION
a. Hematological laboratory procedures are based upon the examination of
blood specimens. To obtain valid test results, specimens must be properly collected,
processed, and recorded. Blood specimens are usually obtained by either venous or
capillary puncture. The source of the specimen is determined chiefly by the quantity of
blood required to perform the laboratory procedures and the age and condition of the
patient.
b. There is generally little difference in blood counts performed on venous or
capillary blood if a free-flowing capillary blood specimen is obtained. Valid blood counts
cannot be made when capillary specimens are not taken from a free-flowing sample or
when they are obtained from cyanotic or calloused areas or areas of local stasis. White
blood cell counts made on blood obtained from such sources can vary as much as
1000-1500 cells per cu mm from their real value. For general purposes, however,
venous samples are preferable since they allow for multiple and repeated hematological
examinations and provide a sufficient quantity of blood for performing any other required
laboratory procedure. Further, with venous blood the chances of error are reduced
because operations are made under ideal conditions and repeat operations are
possible. In situations where there are limitations on the quantity of blood that can be
obtained, that is, in small infants or extensive burn cases, microquantitative methods
are satisfactory for performing an analysis on a specimen obtained by capillary
puncture.
3-2.
VENIPUNCTURE
a. Site. To obtain blood by venipuncture, draw the specimen directly from a
patient's vein with a sterile hypodermic needle and syringe or a vacuum blood sample
device. In adults use the veins located in the proximal forearm or antecubital space as
illustrated in figure 3-1. In infants employ the jugular or femoral vein for the
venipuncture. The vein selected should be large, readily accessible, and sufficiently
close to the surface to be seen and palpated. If venipuncture poses a problem due to
the age of the patient, sclerotization due to repeated venipuncture, or any other unusual
circumstance, the technician should consult a physician concerning the procedure.
UNDER NO CIRCUMSTANCES SHOULD A TECHNICIAN WITHDRAW BLOOD
FROM A SAGITTAL SINUS, JUGULAR VEIN, OR FEMORAL VEIN. This should be left
to the discretion of the physician in charge. Occasionally, the best vein is found on the
hand, leg, or foot. These areas are more sensitive, and the veins are not as firmly
anchored as those of the arm. Veins can become distended and easier to enter by
allowing the arm to hang down for 2 or 3 minutes, by massaging the blood vessel
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3-2