Acute leukemia with a very high leukocyte count: confronting a medical emergency.

From 5% to 30% of adult patients with acute leukemias present with hyperleukocytosis--very high white blood cell counts (> 100,000 cells/mm3)--and symptoms of leukostasis. These conditions are a medical emergency that needs prompt recognition and initiation of therapy to prevent respiratory failure or intracranial hemorrhage. Patients should be referred as soon as possible for induction chemotherapy and leukapheresis.