Normal, mature RBCs are biconcave, disc-shaped, anuclear cells measuring approximately 7–8 microns in diameter on a peripheral blood smear with an internal volume of 80–100 femtoliters (fL). The term used to describe RBCs of normal size is "normocytic." When judging red cell size on a blood smear, the classic rule of thumb is to compare them to the nucleus of a small normal lymphocyte, which has an approximate diameter of 8 microns. Note that this method is not foolproof, as red cells with less than the normal hemoglobin content tend to flatten out more on a slide and may appear larger.
On a Wright-stained peripheral blood smear, normal mature RBCs that contain sufficient hemoglobin have a red-orange appearance with a central pallor (lighter area inside of the cell) no larger than 3 microns in diameter. The term used to describe RBCs of normal color is "normochromic." Normocytic, normochromic cells appearing on a Wright-stained peripheral blood smear are shown in the image on the right.
Normal functioning RBCs survive for approximately 120 days in the peripheral blood circulation before being removed by the liver or spleen. Under normal circumstances, the body produces enough RBCs each day to offset the removal of senescent (old) cells.
RBCs must deform in order to pass through the smallest blood vessels. The deformability of normal RBCs comes from their flexible membranes.
Certain disease states can alter normal RBC characteristics. This course will describe various RBC morphologic changes and correlate the changes with specific disease states or conditions.
