Mild leukocytosis correlates with bacterial, fungal, and chlamydial infections. Moderate elevations can be caused by yolk peritonitis, granulomatous disease, and some phases of septicemia. Of course these counts are rated differently in various species. Leukemia must be included in the differential diagnosis of very high leukocyte counts, but cannot be easily ruled out without repeated morphologic examination of peripheral and bone marrow elements. Leukopenia Leukopenia must be interpreted in conjunction with knowledge of typical reference ranges for the species examined.
Smaller birds tend to have lower normal leukocyte counts.
In any species, a total leukocyte count which is less than 3000 should create concern. The main rule-out for avian leukopenia involves sample artifacts. Whole blood that clots before placement in anticoagulant will yield reduced counts. Lysis of leukocytes before analysis, due to excessive shipping and storage times can result in pseudoleukopenia. True leukopenia usually stems from an overwhelming bacterial infection, severe viral disease, or occasionally toxic substances.