Leukogram abnormalities as prognostic indicators in birds: Association with mortality and proposal of clinically applicable cut-off values.

The complete blood count is one of the most useful complementary tests for monitoring the general condition of birds in veterinary practice. Hematological findings have been widely used to assess disease severity and prognosis in several animal species; however, their prognostic value in birds remains poorly defined. This study aimed to evaluate the association between leukogram abnormalities and clinical outcome in birds treated at a veterinary hospital, with particular emphasis on the risk of death or euthanasia. Medical records from an electronic database were retrospectively reviewed for different bird species admitted between 2017 and 2022. A total of 142 birds with complete blood count results at hospital admission were included. Statistical analysis demonstrated that the presence of band heterophils, metamyelocytes, myelocytes, toxic heterophils of different degrees, and transitional or degenerative left shift was associated with an increased risk of death or euthanasia. Receiver operating characteristic (ROC) curve analysis established discriminatory cut-off values for total immature heterophils (>4%), the mature-to-immature heterophil ratio index (<4.86), the heterophil-to-lymphocyte ratio (>4), absolute band heterophil count (>268/µL), relative metamyelocytes (>1%), and relative band heterophils (>4%). These findings indicate that blood smear evaluation may provide clinically useful prognostic information, particularly through the identification of immature heterophils and toxic changes. In addition, the results reinforce the importance of accurately classifying left shifts, as patterns that do not fit the regenerative classification should be interpreted with caution because of their association with a higher risk of death or euthanasia.