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 noncardiovascular 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 Measure: 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. Conclusion: 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.