Sex and Race-Ethnicity Secular Trends in Mean and Elevated Red Blood Cell Distribution Width Among Adults in the United States, 1999-2012

OBJECTIVE: Red blood cell distribution width (RDW) has been shown to associate with increased risk of cardiovascular and non-cardiovascular death. To our knowledge, no study has examined secular trends in RDW over the last decade. DESIGN: Serial cross-sectional design. SETTING: Data from the National Health and Nutrition Examination Survey (NHANES), 1999-2012, were used. PATIENTS: 34,171 adults. MAIN OUTCOME MEASURES: RDW was assessed from a blood sample derived from the coefficient of variation of the red cell volume distribution histogram and reported as a percent. Elevated RDW was defined as an RDW > 14.6%. RESULTS: The overall age-adjusted mean RDW increased progressively and significantly (P<.05) from 12.59% in 1999-2000 to 12.89% in 2011-2012. The overall age-adjusted prevalence of elevated RDW increased progressively and significantly (P<.05) from 4.01% in 1999-2000 to 6.25% in 2011-2012. Statistically significant increases over this time period also occurred among non-Hispanic White women, non-Hispanic Black men and women, and Mexican American men and women. Across all sex and race-ethnicity combinations, women, compared with men, had higher RDW and larger increases over time in mean and elevated RDW. CONCLUSIONS: Mean and elevated RDW has progressively increased from 1999-2012 among adults in the United States, with increases observed among non-Hispanic Whites, Blacks, and Mexican Americans. Future research is needed to describe the determinants and implications of this RDW rise, as well as explanations for why a greater RDW change has occurred among women.