A light stratum of blood seen when the blood is centrifuged or allowed to stand in a test tube. The red blood cells settle to the bottom and, between the plasma and the red blood cells, a light-colored layer contains mostly white blood cells. Platelets are at the top of this coat; the next layers, in order, are lymphocytes and monocytes; granulocytes; and reticulocytes. In normal blood, the buffy coat is barely visible; in leukemia and leukemoid reactions, it is much larger.

Figure: BUFFY COAT
Buffy coat (arrow) in leukemia