Absolute heterophilias often are the primary contributors to leukocytosis. Expect to see heterophilia in acute inflammatory and infectious processes, including chlamydial, bacterial, and fungal infections. Artifactual heteropenia can follow poor blood smear techniques, resulting in smudge cells. Differential diagnosis for absolute heteropenia includes bacterial sepsis and severe viral disease. In bacterial sepsis, immature heterophils with toxic and degenerative changes may be seen.
Intracellular bacteria indicates bacterial sepsis.
Extracellular bacteria may be artifactual. In viral disease, the patient commonly presents hours from death. The typical hemogram shows the virtual absence of heterophils, with lymphocytes predominating in number. Heterophil morphology exerts an important influence when evaluating the hemogram. A fair amount of variability occurs in color tones depending on the staining protocol used, so morphologic changes are not universally agreed upon.