The blood is primarily made up of red blood cells also called erythrocytes (E). Erythrocytes, which are about 7 microns in diameter, lack a nucleus so they appear as pale red discs. The second most common blood cell in a typical blood smear is a neutrophil (N), a phagocytic white blood cell that has a multilobed nucleus and is two to three times larger than an erythrocyte.
The third most common blood cell is the lymphocyte (L), the B and T cells, which is distinguished by its very large round nucleus. Also, it is about the same size as the erythrocytes (E).