Page 322 - The Veterinary Laboratory and Field Manual 3rd Edition

Haematology 291

example, Babesia sp. Theileria sp. and Rickettsia). Deficiency of iron, or other components
Normal values for the red cell indices of com- of haemoglobin, or deficiency of proteins and
mon domestic species are shown in Tables other nutrients may deplete bone marrow of the
5.3 and 5.4 along with the normal white cell precursors required to produce more red cells,
parameters. especially if demand is high. Healthy animals
respond to blood loss by releasing immature red
cells (reticulocytes) into the blood and these
anaemia cells may still have their nucleus (nRBC) or have
a basophilic stippling (purple spots over the sur-
Red cells (erythrocytes) contain haemoglobin, face as seen in Giemsa stained preparations). In
which is responsible for oxygenating the blood. many types of anaemia, the red cells may vary
Anaemia is a shortage of either red cells or of in size (aniocytosis) and shape (poikilocytosis).
haemoglobin. As anaemia progresses the animal In most mammals, the red cells in the circula-
may become very weak and the mucous mem- tion are of a uniform size, circular (like a disc)
branes become visibly pale. Oxygen is essential in shape and have no nucleus. As noted earlier,
for most metabolic functions in the body. Red in birds and reptiles the red cells are elliptical in
cells circulate in the blood stream providing an shape and have a prominent nucleus.
oxygen supply to tissues and when they are aged
they are removed from the circulation by the Packed cell volume (PCV)
spleen and the breakdown products are recycled
by the liver. Parasitized and abnormal red cells Packed cell volume is the volume of red cells
are also removed from the circulation. Anaemia per 100 ml of blood. The PCV provides a useful
can occur when there is rapid removal or destruc- preliminary assessment of a case of suspected
tion (for example, intravascular haemolysis) of anaemia (indicated by a low PCV). Whole blood
circulating red cells (as in anaplasmosis, Babesia samples collected in EDTA anticoagulant should
infections, immune mediated haemolytic anae- be used for the determination of PCV.
mias and in some toxic insults) or when the There are two commonly used methods,
production of new red cells is delayed (that is, the Wintrobe method and the microhaemato-
in iron deficiency anaemia and in malnutrition). crit method. If a microhaematocrit centrifuge
In haemolytic diseases such as anaplasmo- is available the latter is the preferred method.
sis, where many red cells are broken down over However, the Wintrobe method has the advan-
a short period of time, the liver may become tage of providing additional information as
overwhelmed and waste products enter the cir- outlined below.
culation. If waste products such as bile, which
is formed from degradation of haemoglobin, WIntrobE MEtHod
accumulate in the body tissues these tissues can Wintrobe tubes should have a graduated surface
turn yellow. This is known as jaundice and is divided into 1.0 mm intervals to 100 mm. These
usually evident on examination of the mucous should be kept clean and dry and washed imme-
membranes. The iron from the haemoglobin diately after use. The tubes are filled to the top
is re-used but other components are normally with EDTA blood using a Pasteur pipette and
excreted from the biliary system into the intes- centrifuged at 4000 rpm for 30 min. In order to
tine giving faeces a typical brownish colour avoid breakages make special tube holders to
(more information is given in the biochemistry allow the tubes to fit securely into the centrifuge
section of Chapter 7). cups. When reading the result, the height of the

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