Table 1. Age-adjusted a mean red blood cell distribution width among adults in the National Health and Nutrition Examination Survey, 1999-2012 (N=34,171).
| Mean Red Blood Cell Distribution Width (95% CI), % | |||||||||
| 1999-2000 | 2001-2002 | 2003-2004 | 2005-2006 | 2007-2008 | 2009-2010 | 2011-2012 | %Change b | P c | |
| Overall Sample | 12.59 | 12.65 | 12.66 | 12.73 | 12.74 | 12.79 | 12.89 | .3 | <.001 |
| (12.54-12.64) | (12.60-12.69) | (12.61-12.71) | (12.67-12.78) | (12.68-12.80) | (12.73-12.86) | (12.80-12.97) | |||
| Overall – Men | 12.56 | 12.56 | 12.59 | 12.62 | 12.61 | 12.67 | 12.76 | .2 | <.001 |
| (12.50-12.62) | (12.51-12.60) | (12.53-12.64) | (12.56-12.67) | (12.55-12.66) | (12.60-12.73) | (12.69-12.83) | |||
| Overall - Women | 12.63 | 12.74 | 12.74 | 12.83 | 12.87 | 12.92 | 13.01 | .38 | <.001 |
| (12.56-12.70) | (12.67-12.81) | (12.68-12.80) | (12.77-12.89) | (12.79-12.94) | (12.83-13.00) | (12.91-13.12) | |||
| Non-Hispanic White | |||||||||
| Men | 12.49 | 12.5 | 12.52 | 12.53 | 12.56 | 12.6 | 12.68 | .19 | <.001 |
| (12.42-12.56) | (12.45-12.55) | (12.45-12.59) | (12.49-12.57) | (12.49-12.62) | (12.52-12.68) | (12.60-12.77) | |||
| Women | 12.47 | 12.6 | 12.57 | 12.67 | 12.73 | 12.74 | 12.83 | .36 | <.001 |
| (12.37-12.57) | (12.52-12.68) | (12.52-12.62) | (12.61-12.73) | (12.64-12.82) | (12.64-12.82) | (12.71-12.96) | |||
| Non-Hispanic Black | |||||||||
| Men | 13 | 13.03 | 13.02 | 13.16 | 13.1 | 13.2 | 13.2 | .2 | .001 |
| (12.87-13.13) | (12.92-13.14) | (12.93-13.10) | (13.07-13.25) | (12.98-13.21) | (13.05-13.36) | (13.08-13.31) | |||
| Women | 13.24 | 13.5 | 13.56 | 13.7 | 13.55 | 13.8 | 13.64 | .4 | <.001 |
| (13.13-13.35) | (13.33-13.67) | (13.41-13.71) | (13.54-13.87) | (13.41-13.69) | (13.65-13.96) | (13.46-13.82) | |||
| Mexican American | |||||||||
| Men | 12.5 | 12.48 | 12.54 | 12.51 | 12.54 | 12.64 | 12.76 | .26 | <.001 |
| (13.43-12.56) | (12.41-12.55) | (12.45-12.63) | (12.46-12.57) | (12.46-12.63) | (12.51-12.77) | (12.66-12.86) | |||
| Women | 12.77 | 12.91 | 12.93 | 12.97 | 12.95 | 13.01 | 13.32 | .55 | <.001 |
| (12.73-12.82) | (12.72-13.10) | (12.80-13.07) | (12.75-13.19) | (12.84-13.05) | (12.87-13.15) | (13.10-13.54) | |||
a. Age adjustment was performed using the direct method using the projected year 2000 US Population aged ≥20 years.
b. Percent change was calculated as percent change from 1999-2000 (T1) to 2011-2012 (T2): [T2-T1].
c. Tests for linear trend were conducted using linear-specific orthogonal polynomial coefficients.
N = 34,171; 1999-2000 (n=4210), 2001-2002 (n=4775), 2003-2004 (4530), 2005-2006 (n=4508), 2007-2008 (5358), 2009-2010 (n=5753), 2011-2012 (n=5037).
The weighted mean (SE, standard error) age between 1999 and 2012 was 46.7 yrs (.22). The weighted mean (SE) age across 7 two-year cycles, respectively, were 46.0 (.5), 46.3 (.5), 46.4 (.5), 46.8 (.7), 47.0 (.4), 47.0 (.4) and 47.4 (.8). The weighted proportion (SE) of women between 1999 and 2012 was 52.0 (.2). The weighted (SE) proportion of women across the 7 two-year cycles, respectively, were 52.0 (.6), 52.2 (.5), 51.9 (.7), 52.1 (.5), 52.0 (.5), 51.8 (.5) and 52.1 (.7). The weighted proportion (SE) of Whites between 1999 and 2012 was 70.5 (1.2). The weighted (SE) proportion of Whites across the 7 two-year cycles, respectively, were 69.9 (2.6), 72.9 (2.5), 72.5 (3.3), 72.4 (2.7), 70.1 (3.6), 68.7 (3.3), and 67.1 (3.8). The weighted proportion (SE) of Blacks between 1999 and 2012 was 10.7 (.6). The weighted (SE) proportion of Blacks across the 7 two-year cycles, respectively, were 10.5 (1.6), 10.0 (1.6), 10.8 (1.7), 11.1 (1.9), 10.3 (1.8), 10.8 (.8) and 10.9 (2.2). The weighted proportion (SE) of Mexican Americans between 1999 and 2012 was 7.8 (.6). The weighted (SE) proportion of Mexican Americans across the 7 two-year cycles, respectively, were 7.3 (1.5), 6.8 (.8), 7.6 (1.9), 7.9 (.9), 8.4 (1.5), 8.5 (2.1) and 7.7 (1.7).