20 May 2019
Francesco Cian discusses another interesting case in his latest haematology hub.
Francesco Cian
Job Title
Figure 1. The cat’s blood smear, Wright-Giemsa stain 50×.
The image (Figure 1; Wright-Giemsa 50×) and the haematologic data (Table 1) are from an ethylenediamine tetra-acetic acid blood sample of an adult, domestic shorthair cat with clinical history of depression, acute polypnoea and evidence of regenerative anaemia.
Based on the data and blood smear picture provided, try to answer the following questions:
The pathogenesis of regenerative anaemia includes haemorrhage, which can be external or internal, and haemolysis. Both these conditions stimulate haematopoiesis within the bone marrow, causing the release of new red blood cells into the blood stream – in particular, slightly immature forms, called reticulocytes.
The distinction between these two processes is based on a combination of clinical history (for example, blood loss), blood smear examination and further diagnostic tests (for example, Coombs test).
Examination of the monolayer of this blood smear shows a subjective reduction in the red blood cell density, which confirms the anaemia reported by the automated analyser.
Interestingly, most of the red blood cells are also characterised by small, round, pale pink projections on the surface of the cells (red arrows). These structures are known as Heinz bodies and are aggregates of oxidised, precipitated haemoglobin. They may be present in low percentages (approximately five per cent) in the peripheral blood of healthy cats; however, an increase in number is indicative of oxidative damage, which can also lead to (haemolytic) anaemia.
With new methylene blue stain (Figure 2), they appear as very distinctive, dark blue, round structures (black arrows).
Several reasons exist as to why cats are more prone than dogs to having Heinz bodies in the peripheral blood. Feline haemoglobin is more susceptible to oxidative damage and cat spleen might be less effective in their removal from the circulation.
A common cause for haemolytic anaemia due to oxidative damage is ingestion of products containing onions, as seen here.
This cat was recently rehomed and developed a capricious appetite, possibly due to stress. For several weeks, the new owners fed the cat baby food, which contained significant amounts of onion powder.
