Hypochromic ( lack of colour ) erythrocytes have only a rim of haemoglobin , with central pallor taking up 75 % of the cell .

Anisocytosis is a variation in the size of the cells . The more relative variation there is in red cell size , the greater the anisocytosis . Immature cells are often larger than mature cells , so increased anisocytosis is often associated with regeneration . This change in size encompasses both small and large erythrocytes .

Microcytic cells are seen as a low MCV on an automated analyser . In the blood film , these erythrocytes appear as small normochromic or slightly pale hypochromic cells . As a guide , microcytic cells appear approximately half the size of a lymphocyte .

These are generated by some automated haematology analysers but can also be performed manually , which is a much more sensitive way of monitoring and evaluating regeneration .

Crenation is when erythrocytes have regular , even projections all over their surface ( Figure 3 ). Most commonly these are artefactual , due to prolonged EDTA storage . Crenation is the most common change in blood cell shape .

Macrocytic cells are seen as an elevated MCV . These can be difficult to identify in the blood film but , as a guide , macroytic cells appear approximately twice the size of a lymphocyte .

Polychromasia , by definition , means ‘ many coloured ’. Cells appear blue-purple on the blood film ( Figure 2 ).

Figure 3 . Crenated red blood cell .

Schistocytes are red cell fragments . They are smaller than erythrocytes and are very irregular in shape ( Figure 4 ). They are often seen with microvascular disease and disseminated intravascular coagulopathy ( DIC ) due to fibrin formation and red cell shearing .

Figure 2 . Polychromatophilic red blood cell .

Polychromasia is a feature of immature red blood cells and specifically reticulocytes in circulation . Reticulocytes are slightly larger than erythrocytes , and are blue-purple in colour after staining .

They are rarely seen in healthy cats (< 0.5 %). Increased numbers are seen in regenerative anaemia , but a grading system should be used when assessing the level of regeneration , ensuring that 2 – 3 days have elapsed to allow time for the bone marrow to respond .

If the anaemia does not appear regenerative , because no polychromasia is seen on the blood film , then the next step would be to perform a reticulocyte count .

Figure 4 . Schistocyte .

46 Veterinary Nursing Journal