[Malignant or benign hyperleukocytosis ?].

Leukocytosis or an increase of white blood cells in the peripheral blood is a frequent anomaly. It is important to immediately distinguish if it is a benign or malignant leukocytosis and the analysis of the blood formula is the first step. The presence of abnormal cells such as blast cells is an alarm which must immediately consider the diagnosis of leukemia, and medullogram has to be performed.