Hyperleukocytosis refers to a laboratory abnormality that has been variably defined as a total leukemia blood cell count greater than 50 x 109/L (50,000/microL) or 100 x 109/L (100,000/microL). In contrast, leukostasis (also called symptomatic hyperleukocytosis) is a medical emergency most commonly seen in patients with acute myeloid leukemia (AML) or chronic myeloid leukemia (CML) in blast crisis. It is characterized by an extremely elevated blast cell count and symptoms of decreased tissue perfusion.
Leukostasis is a pathologic diagnosis in which white cell plugs are seen in the microvasculature. Clinically, leukostasis is typically diagnosed empirically when a patient with leukemia and hyperleukocytosis presents with respiratory or neurological distress. Prompt treatment is indicated since, if left untreated, the one-week mortality rate is approximately 20 to 40 percent.
The epidemiology, clinical presentation, diagnosis, and management of hyperleukocytosis and leukostasis will be reviewed here. Other complications of leukemia are presented separately. (See "Overview of the complications of acute myeloid leukemia" and "Overview of the complications of chronic lymphocytic leukemia".)
The incidence of hyperleukocytosis and leukostasis vary by leukemia type and patient population. In general, symptoms of leukostasis are more common in leukemias with large, poorly deformable blasts, such as acute myeloid leukemia.
●Acute myeloid leukemia – Hyperleukocytosis is present in 10 to 20 percent of patients with newly diagnosed acute myeloid leukemia (AML). It is more common in patients with myelomonocytic (FAB-M4) leukemia, monocytic (FAB-M5) leukemia, or the microgranular variant of acute promyelocytic leukemia (FAB-M3) . Symptoms of leukostasis occur less frequently and typically affect patients with white blood cell (WBC) counts over 100 x 109/L (100,000/microL).