title: Platelet counts differ by sex, ethnicity, and age in the United States.
abstract: OBJECTIVE
  The aim of the study is to show that differences in platelet counts by ethnicity, sex, and age are not explained by environmental factors.
  
  
  METHODS
  This is a cross-sectional population-based study of participants in the Third National Health and Nutrition Examination Survey. Our analytic sample included 12,142 participants, of whom 65% were women, 27% were non-Hispanic blacks, and 27% were Mexican Americans. We report weighted geometric mean platelet counts stratified by ethnicity, sex, and age and controlled for indicators of nutritional deficiencies and inflammation.
  
  
  RESULTS
  The lowest mean platelet counts were in whites (260x10(3)/microL; 95% confidence interval [CI], 256-264), and the highest were in non-Hispanic blacks (281x10(3)/microL [95% CI, 276-286]). Older men and women of each ethnicity consistently had lower platelet counts than young adults; 60- to 69-year-olds had mean counts 7x10(3)/microL lower (p<0.001) and 70- to 90-year-olds had counts 18x10(3)/microL lower (p<0.001). Even controlling for iron deficiency, women had higher platelet counts than men (275x10(3)/microL; 95% CI, 271-279) versus 256x10(3)/microL (95% CI, 251-260; p<0.001).
  
  
  CONCLUSIONS
  Platelet count differences by sex, ethnicity, and age are not explained by environmental covariates known to influence platelet count.
authors.affiliation: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. jsegal@jhmi.edu
authors.forename: Jodi B
authors.initials: JB
authors.lastname: Segal
authors.forename: Alison R
authors.initials: AR
authors.lastname: Moliterno
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood; D044383:Black People; D001792:Blood Platelets; D003430:Cross-Sectional Studies; D005006:Ethnicity; D005260:Female; D006801:Humans; D007249:Inflammation / Q000097:blood* / Q000453:epidemiology / Q000208:ethnology; D008297:Male; D017058:Mexican Americans; D008875:Middle Aged; D009748:Nutrition Disorders / Q000097:blood* / Q000453:epidemiology / Q000208:ethnology; D009749:Nutrition Surveys; D010976:Platelet Count / Q000379:methods*; D012016:Reference Values; D012727:Sex Characteristics; D014481:United States / Q000453:epidemiology; D044465:White People; D001741:Black or African American