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 25-28 September, 2018 | Singapore
Morphological abnormalities seen in erythrocytes
· Excessive polychromasia. Polychromasia is an indicator of the patient’s erythrocyte regenerative abilities. Although some polychromasia (1–5%)
is normal, excessive polychromasia indicates a regenerative response to blood loss or anaemia.
· Reticulocytosis, especially when combined with increased polychromasia, is seen as a regenerative response to blood loss or anaemia.
· Anisocytosis. Variation in the size of erythrocytes is occasionally seen in peripheral blood smears as a normal finding. However, the number increases in response to anaemia.
· Poikilocytosis, or variable cell shapes, may represent artefactual error, but is also seen when severe systemic infections affect the bone marrow. Erythrocytes may appear round, elongated or irregular. The nucleus may vary in appearance, location and number. Erythrocytes that appear round with oval nuclei are indicative of accelerated erythropoiesis. Binucleated erythrocytes may also indicate abnormal erythropoiesis in association with severe, chronic inflammatory processes and neoplasia. Poikilocytes are susceptible to damage, and therefore have a shorter life.
· Erythrocytic ballooning has been reported to
be commonly associated with, although not pathognomonic for, lead toxicosis in birds. It
is also seen with ‘conure bleeding syndrome’. There are bulges in the normal ellipsoid shape of the erythrocyte, often accompanied by areas of hypochromasia.
· Haemopararasites are occasionally seen in the erythrocyte cytoplasm of wild-caught birds and reptiles, or those exposed to biting insects.
The white blood cell (WBC) count and differential are important tools in assessing a patient’s response to disease or injury. The WBC count in birds and reptiles can be determined using three testing methods:
· An automated count, which has recently become available in some laboratories.
· An estimated WBC count determined from a blood smear by counting all leucocytes in 10 high-power (40×) microscopic fields, dividing by the number of fields, and then multiplying this average by 2,000, giving a total WBC/μl.
· The Unopette method using phloxine B stain and
a haemocytometer to count eosinophils and het- erophils. This count is compared with the percent- ages of these cells in the differential and the WBC count is calculated using the formula: WBC = (Total Het + Eos) / (% Hets + % Eos) × 100. (Note: In late 2007 the Unopette system was discontinued by the manufacturer. An alternative test in the Avian Leuko- pet®, Vetlab)
Leucocytosis can be normal in young animalss, but it can also be due to:
· Stress. 530
· Inflammation, often associated with bacterial and fungal infections.
Leucopaenia can be due to:
· Chronic inflammation or disease, often with an acute decompensatory episode at the time of presentation.
· Overwhelming bacterial and viral infections
· Artefacts resulting from poor sample handling
White cell differential counts are best obtained from fresh blood smears, as cellular morphology can be affected by anticoagulants in blood collection tubes. A differential count is typically obtained by examination of stained smears under high magnification. Both the type and morphology of the white cells seen are recorded.
In many cases the differential count and cellular morphology give more indication of a bird’s health status than the total white cell count.
The heterophil is the avian and reptile equivalent of the mammalian neutrophil. While it has a similar function to the neutrophil, morphologically it appears quite different. The nucleus contains coarsely clumped chromatin
and usually has two to three lobes. The cytoplasm contains eosinophilic, spherical, oval or spindle-shaped granules. It is, in most species, the predominant white cell. Heterophils lack lysozyme which is why birds form caseated, rather than liquid, pus. Abnormal changes seen with heterophils include:
· Heterophilia
· Heteropaenia
· Toxic heterophils (increased cytoplasmic ba- sophilia, vacuolization, nuclear degeneration, degranulation or abnormal granules)
· Immature (band) heterophils Eosinophils
The eosinophil is a round cell with a slightly basophilic cytoplasm (in contrast to the colourless cytoplasm of the heterophil). The granules are usually rounded, although shape and colour may vary greatly between species. The granules are distinctly eosinophilic and brighter in colour when compared with the heterophil granules. The function of eosinophils is still largely unknown; eosinophilia is rare, sometimes associated with parasitic infections but more commonly with marked tissue damage.
(blood clotting) or technique.

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