g. Allow the blood film to air-dry completely. Do not blow on the slide in an effort
to enhance drying.
h. Using a lead pencil, write the name (or identification) of the patient in the thick
area of the smear. Do not use a wax pencil as it dissolves during the staining process.
a. Cover the slide completely with Wright's stain and allow it to remain on the
smear for about 2 minutes to fix the blood cells. The stain should cover the slide but
should not be allowed to overflow the edges; the stain must be replenished should it
begin to evaporate.
b. Add an equal volume of Wright's stain buffer directly to the stain and blow the
mixture gently to assure maximum mixing. Allow it to remain for about 4 minutes.
The times recommended for staining and buffering are approximate and
should be adjusted with each fresh batch of stain to give the most satisfactory
c. Using tap water, float off the mixture of stain and diluent from the slide to
avoid the deposition of metallic scum on the smear. The scum appears after the
addition of the buffer to the stain. Wash the slide thoroughly under cold, slowly-running
d. Air dry the smear and wipe the excess stain from the under surface of the
(1) A properly prepared blood smear is margin-free; has no lines, ridges, or
holes; is placed centrally on the slide; has an adequate thin area; and has a uniform
distribution of leukocytes.
(2) It is preferable that blood smears not be made from blood containing
anticoagulants since the leukocytes change their staining characteristics, develop
vacuoles, engulf oxalate crystals, and show nuclear deformities. However, satisfactory
slides are made with blood anticoagulated with EDTA.
Avoid the following errors:
(a) Thick films made from an excess amount of blood placed on the
(b) Delay in transferring the blood to the slide.