Page 312 - The Veterinary Laboratory and Field Manual 3rd Edition

Haematology 281

Granulocytes Basophils
Granulocytes include the polymorph neutrophils Basophils contain basophilic (blue/basic) stain-
(PMN), eosinophils and basophils and avian/ ing granules. Depending on the species these
reptilian heterophils. range from a very pale grey (cats) to deep blue
(horses). They are not common.

Neutrophils
Neutrophils may contain granules but they do 5.2 Collection of specimens
not stain with Romanowsky stains. The nucleus
usually has three or more lobes but in times of For haematology, blood is usually collected from
excess production (for example, due to infec- the neck (jugular vein) in cattle (see Figures
tion) band forms of nuclei are seen as well as 1.18b–d), horses, sheep and goats and from the
segmented forms. When many ‘band’ forms are front leg (brachiocephalic vein) in the dog and
1
present this is known as a ‘shift to the left’. In cat. If haemoparasites are suspected then blood
acute bacterial diseases, the proportion of neu- smears should also be made from blood collected
trophils may increase (neutrophilia) and the from peripheral vessels such as the ear vein (in
total white cell count may also increase (leuko- large animals). Blood for haematology should
cytosis). In chronic diseases, this may not occur be collected into anti-coagulant (for example,
2
because white cells can become sequested in ethylene-diaminetetra-acetic acid (EDTA ), hep-
tissues and the production of new white cells arin or sodium citrate) to prevent clotting. For
can be interrupted if essential resources become most livestock, a 10 ml sample of blood collected
scarce, for example, in severely debilitated and into one or more vacutainers is ideal for labora-
malnourished animals. Neutrophils form a large tory testing. If commercial vacutainers are not
component of ‘pus’, which is a thick protein rich available, or vacutainers are re-used, they may be
material that also contains necrotic material and prepared in the laboratory but it is important to
cellular debris and is commonly seen in tissues make sure that there is sufficient vacuum pres-
infected with bacteria. The number of circulat- ent. Vacutainers containing EDTA have purple
ing neutrophils may also increase when animals tops; those with heparin have green tops (see
are exposed to physiological stress, for example, also Chapter 7). It is important to collect at least
crowding or handling so it is important to mini- 5 ml of blood for full haematology although for
mize stress when blood samples are collected. some tests, especially for small animals and
birds, smaller volumes (2 ml) may be acceptable.
Smaller volumes can also be used if automated
Eosinophils microtitre systems are available, these systems
use the principles of flow cytometry to measure
Eosinophils contain eosinophilic (acid/pink)
staining granules. They are more numerous in the size and number of cells but they do need
some allergic reactions and are attracted by his- to be appropriately calibrated for the species of
tamines which are released from damaged cells. interest (see Chapter 2).
An increase in eosinophils (eosinophilia) can Unclotted whole blood samples are used in
indicate that the animal has a parasitic infection the laboratory to determine the packed cell vol-
(for example, lungworm). ume (PCV), the total red and white cell counts,
the differential white cell count and the haemo-
globin content of the sample. These parameters
can then be used to examine a number of other

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