Overview of Leukocyte Disorders in Animals

Leukocytes, or white blood cells (WBCs), in the blood of healthy mammals include segmented neutrophils, band neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

Observation of neutrophils less mature than bands (eg, metamyelocytes, myelocytes, progranulocytes), blast cells of any hematopoietic lineage, mast cells, and other neoplastic cells is indicative of disease. WBCs vary in their site of production, duration of circulation, and stimuli that prompt their release into and migration out of the vascular system. Differences in leukocyte physiology account for species differences in blood cell concentrations in healthy animals and their responses to disease.

The leukogram, a component of the CBC, is an organized tabulation of the total nucleated cell concentration, along with the concentrations of specific WBC types present in the blood sample, also known as the WBC differential. Knowledge of species-specific WBC physiology and the influence of disease processes forms the basis for interpreting abnormalities of the leukogram to inform a diagnosis. However, most leukogram interpretations define a process rather than a specific diagnosis. Processes generally fall into four groups:

• transient physiological responses that alter vascular hemodynamics

• inflammatory, infectious, and immunological responses

• bone marrow responses to injury

• hematopoietic neoplasia