Journal: The American Journal of Clinical Nutrition

Article Title: Overview of a roundtable on NHANES monitoring of biomarkers of folate and vitamin B-12 status: measurement procedure issues ^{1 2 3 4 5 6}

doi: 10.3945/ajcn.111.017392

Figure Lengend Snippet: Roundtable dialogue: measurement of biomarkers of folate status in NHANES ¹

Article Snippet: The Bio-Rad Quantaphase II procedure (Bio-Rad Laboratories, Hercules, CA) that NHANES 1991–1994 and NHANES 1999–2006 used produced serum and RBC folate results that were, on average, 29% lower for serum and 45% lower for RBC than the MA that NHANES 2007–2010 used. These differences will require adjustment equations to evaluate time trends..

Techniques: Activity Assay, Produced

Journal: The Journal of Nutrition

Article Title: Changes in Measurement Procedure from a Radioassay to a Microbiologic Assay Necessitate Adjustment of Serum and RBC Folate Concentrations in the U.S. Population from the NHANES 1988-2010 ^{1 2}

doi: 10.3945/jn.111.156901

Figure Lengend Snippet: Regression models for blood folate data generated by the BR and the MBA. (A) Finding the best fit for serum folate data in a convenience set of serum samples (n = 325) (4). The dashed vertical line represents the knot for the piecewise linear regression determined through a grid search (39 nmol/L). The correlation coefficients (R2) were as follows: linear, 0.94; piecewise linear, 0.95; and fractional polynomial, 0.95. The regression equations with x = log10BR and y = MBA were as follows: linear, y = 10**(0.847 · x + 0.372); piecewise linear, y = 10**(1.0847 · x + 0.0636) if x ≤1.595 and y = 10**(0.6591 · x + 0.7424) if x >1.595; and fractional polynomial, y = 10**(0.0188 · x3 – 2.7109 · x−1/2 + 3.8276). (B) Linear regression model showing the influence of MTHFR genotype on whole-blood folate in a convenience set of whole-blood samples (n = 171) (5). The correlation coefficients (R2) were as follows: C/C, 0.83; C/T, 0.92; and T/T, 0.80. The regression equations with x = log10BR and y = MBA were as follows: C/C, y = 10**(1.0937 · x + 0.0707); C/T, y = 10**(1.1137 · x + 0.0180); and T/T, y = 10**(0.9441 · x + 0.2924). (C) Finding the best fit for whole-blood folate data in a convenience set of whole-blood samples (n = 171) (4). The dashed vertical line represents the knot for the piecewise linear regression determined through a grid search (229 nmol/L). The correlation coefficients (R2) were as follows: linear, 0.80; piecewise linear, 0.80; and fractional polynomial, 0.80. The regression equations with x = log10BR and y = MBA were as follows: linear, y = 10**(1.0179 · x + 0.2175); piecewise linear, y = 10**(1.1108 · x + 0.0147) if x ≤2.36 and y = 10**(0.8216 · x + 0.6972) if x >2.36; and fractional polynomial, y = 10**(−15.4588 · x−2 * logex – 1.1317 · x−2 + 5.2092). Note: **designates exponential. BR, Bio-Rad radioassay; MBA, microbiologic assay.

Article Snippet: However, a recalibrated Bio-Rad Quantaphase II assay (using a spectrophotometrically verified folic acid calibrator) was introduced in 1993 and was used in the second phase of NHANES III (1991–1994) and in NHANES 1999–2006 ( 3 ).

Techniques: Generated

Journal: The Journal of Nutrition

Article Title: Changes in Measurement Procedure from a Radioassay to a Microbiologic Assay Necessitate Adjustment of Serum and RBC Folate Concentrations in the U.S. Population from the NHANES 1988-2010 ^{1 2}

doi: 10.3945/jn.111.156901

Figure Lengend Snippet: Frequency distribution curves for unadjusted and assay-adjusted serum folate data for NHANES 1988–1994 (A; n = 23,361 unadjusted and 23,359 adjusted), for 1999–2002 (B; n = 15,653 unadjusted and adjusted), and for 2003–2006 (C; n = 15,331 unadjusted and adjusted) and for unadjusted data for NHANES 2007–2010 (D; n = 15,889). Adjustments were performed by regressing Bio-Rad radioassay data from 1988 to 1994 and from 1999 to 2006 to microbiologic assay–equivalent data.

Article Snippet: However, a recalibrated Bio-Rad Quantaphase II assay (using a spectrophotometrically verified folic acid calibrator) was introduced in 1993 and was used in the second phase of NHANES III (1991–1994) and in NHANES 1999–2006 ( 3 ).

Techniques:

Journal: The Journal of Nutrition

Article Title: Changes in Measurement Procedure from a Radioassay to a Microbiologic Assay Necessitate Adjustment of Serum and RBC Folate Concentrations in the U.S. Population from the NHANES 1988-2010 ^{1 2}

doi: 10.3945/jn.111.156901

Figure Lengend Snippet: Frequency distribution curves for unadjusted and assay-adjusted RBC folate data for NHANES 1988–1994 (A; n = 23,402 unadjusted and 22,846 adjusted), for 1999–2002 (B; n = 15,827 unadjusted and 15,613 adjusted), and for 2003–2006 (C; n = 15,451 unadjusted and 15,196 adjusted) and for unadjusted data for NHANES 2007–2010 (D; n = 15,951). Adjustments were made by regressing Bio-Rad radioassay data from 1988 to 1994 and from 1999 to 2006 to microbiologic assay–equivalent data.

Article Snippet: However, a recalibrated Bio-Rad Quantaphase II assay (using a spectrophotometrically verified folic acid calibrator) was introduced in 1993 and was used in the second phase of NHANES III (1991–1994) and in NHANES 1999–2006 ( 3 ).

Techniques: