Red Cell Size

Mean cell size

• Estimated on a peripheral smear by comparing the diameter of the red blood cell (RBC) to the diameter of the nucleus of a small lymphocyte.¹

• The peripheral smear has poor sensitivity for detecting changes in red blood cell size. In a study of 200 consecutive adult patients with an MCV of 100 fL or more, macrocytosis was recognized microscopically in only 111 (65%) out of the 170 patients with a high MCV. In other words, 35% of cases with MCV > 100 fL were missed on blood smear. That’s a large margin of error! 

Variation in cell size

• Anisocytosis defined as increased heterogeneity (or variation) in RBC size regardless of the average RBC diameter.