b. Antithrombin. Heparin is an anticoagulant classified in this group. It works by
interfering with the formation of intrinsic thromboplastin and the formation of thrombin.
c. Capillary tubes. Capillary tubes with a red ring are heparinized. Those with
black or blue rings do not contain anticoagulants.
2-12. FIXATION AND STORAGE
The fixative used for blood smears is methanol. This alcohol prevents the
humidity in the air from lysing the RBC's. Anticoagulated whole blood should be stored at
refrigeration temperatures and not frozen. Freezing will cause hemolysis. Serum for
serological diagnosis should be removed from the red cells and refrigerated or frozen.
2-13. PROCESSING THE BLOOD SMEAR
a. Thin and Thick Blood Smears (Figures 2-3A and 2-3B). The most
satisfactory procedure for the definitive diagnosis of malaria, trypanosomiasis and
filariasis is the use of thick and thin blood films on the same slide. This procedure serves
as a convenient method for forwarding the specimen to another laboratory for
examination or holding the specimen for examination at a later time. It is also a
convenient method for performing field surveys on large numbers of individuals in
(1) Identification. Identify the slide by writing the patient's name or identifying
number on the thickest portion of the thin smear with an ordinary pencil or a diamond
scriber. A minimum of three thick-thin preparations should be prepared from each
(2) Staining. Stain the slides within a day after preparation to get maximum
STEP 1: Use only chemically lean slides, free from grease.
STEP 2: Perform a finger puncture.
STEP 3: Two drops of blood may be placed on the same slide by touching the surface
of the slide to the blood as it wells up from the puncture.
STEP 4: Immediately lay the slide down on a flat surface blood-side up. Smears
should be prepared before the drops begin to dry around the edges. The thin
smear should be made first. A small drop is best for the preparation of the
thin smear, while a larger drop is required for the thick smear.
STEP 5: Hold a second slide, by the edges between thumb and finger, at a 30 degree
angle to the surface of the first slide. Touch one end of the slide just ahead
of the drop of blood.