The Red Cell Histogram and The Dimorphic Red Cell Population

The RBC histogram is an integral part of automated hematology analysis and is now routinely available on all automated cell counters. This histogram and other associated complete blood count (CBC) parameters have been found abnormal in various hematological conditions and may provide major clues in the diagnosis and management of significant red cell disorders. In addition, it is frequently used, along with the peripheral blood film, as an aid in monitoring and interpreting abnormal morphological changes, particularly dimorphic red cell populations. This article discusses some morphological features of dimorphism and the ensuing characteristic changes in their RBC histograms. * CBC : complete blood count RDW : red blood cell distribution width MCV : mean corpuscular volume MCHC : mean corpuscular hemoglobin concentration IDA : iron deficiency anemia RDW-CV : red blood cell distribution width coefficient of variation thal : thalassemia SD : standard deviation HPP : hereditary pyropoikilocytosis * Anisocytosis: : Variation in red cell size. Anomalous pulses: : This is an interference by electrical pulses/noises but at a very low level. These anomalous pulses and coincident doublets are reflected as a small tail to the right of a normal curve ([Figure 1A][1] and [Figure 2A][2]). In most normals, the frequency distribution of red cells does not exceed the range of 50 fL-200 fL. Despite the instrument’s refinement in aperture design, correction for coincidental passage of cells, and the use of sophisticated edit circuitry to exclude aberrant pulses, the presence of these interferences to some degree cannot be avoided. Coincident doublets: : Occasionally, 2 or more cells pass through an aperture at the same time and are counted as a single cell. The analyzer automatically corrects results for coincidence. Dimorphic: : According to the Webster New World College Dictionary, the word dimorphic means the occurrence of 2 types of individuals in the same species (2 different forms/sizes of cells in a sample). Note, however, that the term dimorphic is broadly defined in this article to signify 2 or more (multiple) red cell populations. This is because there are 2 technical meanings for the same word. When “dimorphic” is used, the context will determine the meaning. Poikilocytosis: : Variation in red cell shape. [1]: #F2 [2]: #F3