Benign Monocytic Disorders

Monocytes normally comprise between 2% and 8% of the peripheral blood leukocytes with absolute monocyte count between 0.2 and 0.8 × 109/L, although it has been proposed that absolute counts as low as 0.5 × 109/L should qualify as clonal monocytosis if there is an associated clonal genetic abnormality. Monocytes belong to the mononuclear phagocyte system, spend only a short time in the marrow, and after circulating for 20 to 40 hours, leave the blood to enter solid tissues where they differentiate into macrophages (histiocytes) and survive for months or even years.