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Shifts in MCV

Cold agglutinins Transfusions

Chemotherapy—not all drugs AZT therapy

Hyperglycemia—transient shifts

Cold agglutinins Transfusions

Chemotherapy—not all drugs AZT therapy

Hyperglycemia—transient shifts

26 Part I • Basic Hematology Principles poikilocytosis (variation in shape) in a peripheral smear. The RDW is derived as follows:

(Standard deviation of RBC

volume/mean MCV) X 100

The normal value for RDW is 11.5% to 14.5%. The standard deviation of red cell volume is derived from size histogram data that plot red cell size after a large number of red cells has been analyzed by the instrument. The usefulness of the RDW is that in many cases the RDW will become abnormal earlier in the anemia process than the MCV Because many anemias (like iron deficiency anemias) develop over a period of time, this parameter may provide a sensitive indicator of red blood size change16 before the red cell indices become overtly abnormal.

The final item in the CBC is a platelet count. Information regarding platelet estimates and platelet morphology is given in Chapter 20.

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