Abstract
Leukocytosis is defined by an increased WBC count in the peripheral blood. This can be caused by many pathologies from benign conditions such as stress, infection, and inflammation or malignant origins such as leukemia. Although leukocytosis is regularly encountered clinically and has many etiologies making a definitive diagnosis, at times, may be difficult. A case of severe leukocytosis requires careful consideration of symptoms and confirmation with serial complete blood count (CBC) testing before pursuing further invasive testing such as bone marrow biopsy. Here, we report the case of a 78-year-old male patient who, after a cardiac arrest, presented with reactive hyperleukocytosis mimicking acute monocytic leukemia.