SYNOPSIS
The blood film is one of the world’s most widely used laboratory tests
for screening, case finding, diagnosis, and monitoring of disease. Blood film
is a smear of a blood sample made on a microscope slide to help in diagnosis.
There are about three types of blood films in haematology, which includes; thin
film, thick film and wet film preparation.
Blood film is highly important in
haematology laboratory because it forms the daily routine in a haematology
laboratory. Blood film can be prepared from fresh blood with no anticoagulant
added or from ethylenediaminetetra-acetic acid (EDTA)-anticoagulated blood. For
thin film, a small drop of blood is placed in the centre line of a slide about
1cm from one end. Without delay, a spreader is placed in front of the drop at
an angle of about 30degree to the slide, moved back to make contact with the
drop of blood. In contact, the blood sample is allowed to spread along contact
line. With a steady movement of the hand, the drop of blood is spread along the
slide. The slide is then labeled and allowed to dry. In thick film preparation,
the spreader is lowered at a very steep angle to make the smear on the slide.
For wet preparation, a diluents is utilized to dilute the cells and also stain
some cell properties to enable diagnosis. In staining of thin and thick film,
romanowsky stains are utilized. Mostly used are leishman and giemsa stains. A
good thin film should not have holes, it should not be too thick, it should
have a tail, body and head, it should not be ragged. A good thick film should
reflect the prints on a paper while placed on it.
INTRODUCTION
Blood film making in haematology is one of the
oldest methodology employed in haematology discipline. Starting with the
concept of blood circulation, which was introduced in 1628, numerous advances
have been made in the field of haematology that have significantly improved the
lives of patients with haematologic disorders and blazed a trail for advances
in other fields. One of these advances is the introduction of blood film making
which was also made in 1628 (Barbara, 2005). In late 1940s, a mechanical aid in
making blood films and blood count, alongside with a blood pipette shaking
machine was introduced.
This was a huge success in haematology practices
because it led way to the now automation that has evolved to help in film making
and cell enumeration (Barbara, 2005). Often, the examination of a peripheral
blood smear is the single most useful procedure in haematology. Blood smear is
a haematological test used to provide information concerning drugs and diseases
that affect the morphology of red cells and white cells; and to help diagnose
certain congenital and acquired diseases. (Berend; 2007). In every case where
pathology may be present, it is good clinical practice to make a blood smear
which allows for a detailed examination of the erythrocytes and leucocytes and
a manual white cell differential (Bentley, 2000).
More
so, a properly performed and analysed blood smear is the most informative of
all haematological tests, allowing examination of all cell types. Blood smear
should be made immediately from fresh blood or within one hour of collecting
blood in EDTA anticoagulant. Even though EDTA prevent clotting, the cells
continue to metabolise oxygen and glucose altering the plasma matrix, leading
to cell stress and altering cell morphology often to the point where subtle or
sometimes gross pathological changes cannot be distinguished (Beutler et al.,1999).