Abstract Journal of the American Veterinary Medical Association March 1, 2001, Vol. 218, No. 5, Pages 736-739 doi: 10.2460/javma.2001.218.736 Clinical outcome and diseases associated with extreme neutrophilic leukocytosis in cats: 104 cases (1991–1999) Michael D. Lucroy, DVM, MS, DACVIM Bruce R. Madewell, VMD, MS, DACVIM Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA 95616. (Lucroy, Madewell); Present address is the Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078. (Lucroy) Objective To describe diseases, prognosis, and clinical outcomes associated with extreme neutrophilic leukocytosis in cats. Design Retrospective study. Animals 104 cats with extreme neutrophilic leukocytosis. Procedure Medical records from 1991 to 1999 were examined to identify cats that had ≥ 50,000 WBC/µl with ≥ 50% neutrophils. Signalment, absolute and differential WBC counts, rectal temperature, clinical or pathologic diagnosis, duration and cost of hospitalization, and survival time were reviewed. Results Mean age of cats was 8.3 years, mean WBC count was 73,055 cells/µl, and mean absolute neutrophil count was 59,046 cells/µl. Mean duration of hospitalization was 5.9 days, and mean cost of hospitalization was $2,010. Twenty-nine (28%) cats were febrile, and 63 (61%) cats died. Overall median survival time was 30 days. Cats with neoplasia were nearly 14 times as likely to die unexpectedly as cats with other diseases. Conclusions and Clinical Relevance Extreme neutrophilic leukocytosis was associated with a high mortality rate. The prognostic importance of extreme neutrophilic leukocytosis should not be overlooked. Cats and dogs have similar diseases, mortality rates, and treatment costs associated with extreme neutrophilic leukocytosis. (J Am Vet Med Assoc 2001;218:736–739)