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 diameter of the RBC generally correlates with its volume and average cell red cell size is quantified as the mean cell volume (MCV). 
  • 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 is defined as increased heterogeneity (or variation) in RBC size regardless of the average RBC diameter. It correlates with the red cell distribution width (RDW), which is obtained using an automated hematology analyzer.

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