Leukocytosis is due to increased production of WBCs or increased release of WBCs from bone marrow or blood vessels where many WBCS are stored.

Leukocytosis is commonly seen in infections, physical or emotional stress, and medications (steroids ). It can be seen in chronic heavy smokers. A less common cause is a primary hematologic malignancy. Some patients with chronic idiopathic neutrophilia have WBCs outside the normal range with no identified cause.

Lithium causes an increase in neutrophils leading to neutrophilia and leukocytosis. It is due to both margination of cells into the periphery as well as a direct action of lithium on the bone marrow. The white blood cell (WBC) counts increase, on average, by 2500 cells/μL. It starts with a week of treatment and persists chronically [1]. The WBC typically does not rise above 20,000 cells/μL. Lithium-induced leukocytosis generally requires no intervention. The leukocytosis is sometimes accompanied by thrombocytosis.

Antipsychotics including clozapine can cause a small degree of leukocytosis. Carbamazepine can occasionally cause leukocytosis [2].