Description of the data source, numerator, denominator, survey questions, and other relevant details about the national estimate.
Lower RBC folate concentration is a population weighted estimate from the blood specimens collected from women aged 15 to 44 years as part of the standard NHANES protocol. According to data from the National Health and Nutrition Examination Survey (NHANES), median RBC folate concentrations increased substantially between 1988-94 and 1999-2000, pre- and post-fortification with folic acid, and then declined slightly in the post-fortification period (Pfeiffer et al., 2007, CDC, 2007). In 1999-2000, HP2010 objective 16-16b was met for all nonpregnant US women aged 15-44 y, and for non-Hispanic white and Mexican-American, but not non-Hispanic black women (CDC, 2007). The decreases from 1999-2000 to 2003-2004 were not in the low end of the distribution and thus did not raise concerns about inadequate status. However, continued monitoring remains important. The concentration of RBC folate associated with the lowest neural tube defect risk is unknown (Daly et al., 1995; Wald et al., 1998). In 2007-2010, the 25th percentile of RBC folate among US women aged 15-44 years was 337 ng/ml. Given that folic acid has been shown to reduce NTDs, reductions in the proportion of women with lower RBC folate concentrations should move us towards this goal.
Any change to the objective text, baseline, target, target-setting method or data source since the Healthy People 2020 launch.
In 2013, the baseline was revised from 24.5% (2003-06) to 24.9% (2007-10) because the assay that was used to measure RBC folate concentrations changed after the 2005-2006 NHANES cycle. Through survey year 2006 the Bio-Rad Quantaphase II radioassay (BR) was used, and from 2007 forward the microbiological assay (MA) was used. Although regression equations are provided in the NHANES documentation for converting BR values to MA values, they are dependent on methylenetetrahydrofolate reductase(MTHFR) genotype information, which is not available in the continuous NHANES data. MTHFR genotypes have been found to vary by race/ethnicity and without taking these differences into account the converted BR data do not reflect the true differences between race/ethnicity sub-groups. However, the MA does not have this issue and will be used in future NHANES. The target was adjusted from 22.1% to 22.4% to reflect the revised baseline using the original target-setting method.
Also, the objective text was changed from ‘Reduce the proportion of women of childbearing potential who have low RBC folate concentrations’ to ‘Reduce the proportion of women of childbearing potential who have lower RBC folate concentrations.’ Finally the numerator was changed from ‘Number of non-pregnant women aged 15-44 years with red-blood-cell (RBC) foliate concentration <195 ng/ml, the 25th percentile of RBC concentrations among this group in 2003-2006’ to ‘Number of non-pregnant women aged 15-44 years with red-blood-cell (RBC) folate concentration <337 ng/mL, below the 25th percentile of RBC concentrations among this group in 2007-2010.’
Additional resources about the objective.
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