Platelet counts in three racial groups.

Documented differences exist in red blood cell (RBC) and granulocyte counts between black and white people. However, little comparative information is available on differences in platelet counts in the two racial groups. Therefore, this study was performed to compare platelet counts in healthy white (94), black (92), and Latin-American (63) persons. Black women had significantly higher platelet counts than did white women (P less than 0.025). Latin-American women were between the other two groups. No differences were noted among men. Black women also had a significantly higher prevalence of iron deficiency and microcytosis of RBCs than did white women. After exclusion of women with either microcytosis or iron deficiency, racial differences in platelet counts were no longer evident. The authors conclude that the differences in the platelet counts between black and white women were secondary to common RBC differences (such as iron deficiency and other causes of microcytic anemia) and were not intrinsic to the platelets. These and other factors that can affect platelet counts should be excluded before determining the reference ranges for proper interpretation of the platelet counts.