In this section, we will outline characteristic morphologic changes in blood cells that help us identify disease processes or pathologic mechanisms. Assessment of morphologic features of red and white blood cells and platelets is an essential part of blood smear examination. Examination for morphologic changes in cells is important because these changes can be useful markers of underlying disease or can give clues as to the mechanisms behind cytopenias in peripheral blood. For instance, examination of a blood smear for the presence of polychromasia is a critical component in determining if whether an anemia is regenerative and due to to blood loss or hemolysis. Since animals cannot speak for themselves, we have to let their blood do the talking for them and in many cases, changes in peripheral blood cells can be very helpful for disease diagnosis or directing the diagnostic or treatment plan. This aspect of a hemogram is where the human eye surpasses any machine, because our eyes can detect these changes, whereas a machine generally cannot.
- Erythrocytes: Includes information on species differences, nucleated RBC features, shape changes, size changes, color changes, changes in pattern (e.g. rouleaux), and inclusions (e.g. Heinz bodies). We have also included a quick guide as to what all these changes mean (and what they look like).
- Leukocytes: Includes information on normal leukocytes in blood, such as mature and immature neutrophils (left shift), with image compilations of different mammalian species for each leukocyte, and abnormal features, including toxic change in neutrophils and reactive lymphocytes. An illustration of how we use clinical, hematologic and morphologic criteria of large round cells, “big blue cells“, to classify these cells as potentially reactive or neoplastic (i.e. hematopoietic neoplasia) is also provided (table and diagram format).
- Platelets: Includes information on platelet features in normal animals of different species and changes in platelets, such as platelet clumping and platelet versus fibrin clumps.