Last data update: May 06, 2024. (Total: 46732 publications since 2009)
Records 1-20 (of 20 Records) |
Query Trace: Johnson CL[original query] |
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Interlaboratory validation of an improved method for detection of Cyclospora cayetanensis in produce using a real-time PCR assay.
Murphy HR , Cinar HN , Gopinath G , Noe KE , Chatman LD , Miranda NE , Wetherington JH , Neal-McKinney J , Pires GS , Sachs E , Stanya KJ , Johnson CL , Nascimento FS , Santin M , Molokin A , Samadpour M , Janagama H , Kahler A , Miller C , da Silva AJ . Food Microbiol 2018 69 170-178 A collaborative validation study was performed to evaluate the performance of a new U.S. Food and Drug Administration method developed for detection of the protozoan parasite, Cyclospora cayetanensis, on cilantro and raspberries. The method includes a sample preparation step in which oocysts are recovered from produce using an enhanced produce washing solution containing 0.1% Alconox and a commercially available method to disrupt the C. cayetanensis oocysts and extract DNA. A real-time PCR assay targeting the C. cayetanensis 18S rDNA gene with an internal amplification control to monitor PCR inhibition provides species-specific identification. Five laboratories blindly analyzed a total of 319 samples consisting of 25 g of cilantro or 50 g of raspberries which were either uninoculated or artificially contaminated with C. cayetanensis oocysts. Detection rates for cilantro inoculated with 200, 10, and 5 oocysts, were 100%, 80%, and 31%, respectively. For raspberries, the detection rates for samples inoculated with 200, 10, and 5 oocysts were 100%, 90% and 50%, respectively. All uninoculated samples, DNA blank extracts, and no-template PCR controls were negative. Reproducibility between laboratories and analysts was high and the method was shown to be an effective analytical tool for detection of C. cayetanensis in produce. |
Challenges and lessons learned in generating and interpreting NHANES nutritional biomarker data
Pfeiffer CM , Lacher DA , Schleicher RL , Johnson CL , Yetley EA . Adv Nutr 2017 8 (2) 290-307 For the past 45 y, the National Center for Health Statistics at the CDC has carried out nutrition surveillance of the US population by collecting anthropometric, dietary intake, and nutritional biomarker data, the latter being the focus of this publication. The earliest biomarker testing assessed iron and vitamin A status. With time, a broad spectrum of water- and fat-soluble vitamins was added and biomarkers for other types of nutrients (e.g., fatty acids) and bioactive dietary compounds (e.g., phytoestrogens) were included in NHANES. The cross-sectional survey is flexible in design, and biomarkers may be measured for a short period of time or rotated in and out of surveys depending on scientific needs. Maintaining high-quality laboratory measurements over extended periods of time such that trends in status can be reliably assessed is a major goal of the testing laboratories. Physicians, health scientists, and policy makers rely on the NHANES reference data to compare the nutritional status of population groups, to assess the impact of various interventions, and to explore associations between nutritional status and health promotion or disease prevention. Focusing on the continuous NHANES, which started in 1999, this review uses a "lessons learned" approach to present a series of challenges that are relevant to researchers measuring biomarkers in NHANES and beyond. Some of those challenges are the use of multiple related biomarkers instead of a single biomarker for a specific nutrient (e.g., folate, vitamin B-12, iron), adhering to special needs for specimen collection and handling to ensure optimum specimen quality (e.g., vitamin C, folate, homocysteine, iodine, polyunsaturated fatty acids), the retrospective use of long-term quality-control data to correct for assay shifts (e.g., vitamin D, vitamin B-12), and the proper planning for and interpretation of crossover studies to adjust for systematic method changes (e.g., folate, vitamin D, ferritin). |
The vitamin D status of the US population from 1988 to 2010 using standardized serum concentrations of 25-hydroxyvitamin D shows recent modest increases
Schleicher RL , Sternberg MR , Lacher DA , Sempos CT , Looker AC , Durazo-Arvizu RA , Yetley EA , Chaudhary-Webb M , Maw KL , Pfeiffer CM , Johnson CL . Am J Clin Nutr 2016 104 (2) 454-61 BACKGROUND: Temporal trends in the US population's vitamin D status have been uncertain because of nonstandardized serum 25-hydroxyvitamin D [25(OH)D] measurements. OBJECTIVE: To accurately assess vitamin D status trends among those aged ≥12 y, we used data from the cross-sectional NHANESs. DESIGN: A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for measuring 25(OH)D (sum of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3), calibrated to standard reference materials, was used to predict LC-MS/MS-equivalent concentrations from radioimmunoassay data (1988-2006 surveys; n = 38,700) and to measure LC-MS/MS concentrations (2007-2010 surveys; n = 12,446). Weighted arithmetic means and the prevalence of 25(OH)D above or below cutoff concentrations were calculated to evaluate long-term trends. RESULTS: Overall, mean predicted 25(OH)D showed no time trend from 1988 to 2006, but during 2007-2010 the mean measured 25(OH)D was 5-6 nmol/L higher. Those groups who showed the largest 25(OH)D increases (7-11 nmol/L) were older, female, non-Hispanic white, and vitamin D supplement users. During 1988-2010, the proportions of persons with 25(OH)D <40 nmol/L were 14-18% (overall), 46-60% (non-Hispanic blacks), 21-28% (Mexican Americans), and 6-10% (non-Hispanic whites). CONCLUSIONS: An accurate method for measuring 25(OH)D showed stable mean concentrations in the US population (1988-2006) and recent modest increases (2007-2010). Although it is unclear to what extent supplement usage compared with different laboratory methods explain the increases in 25(OH)D, the use of higher vitamin D supplement dosages coincided with the increase. Marked race-ethnic differences in 25(OH)D concentrations were apparent. These data provide the first standardized information about temporal trends in the vitamin D status of the US population. |
National estimates of serum total 25-hydroxyvitamin D and metabolite concentrations measured by liquid chromatography-tandem mass spectrometry in the US opulation during 2007-2010
Schleicher RL , Sternberg MR , Looker AC , Yetley EA , Lacher DA , Sempos CT , Taylor CL , Durazo-Arvizu RA , Maw KL , Chaudhary-Webb M , Johnson CL , Pfeiffer CM . J Nutr 2016 146 (5) 1051-61 BACKGROUND: The 2007-2010 NHANES provides the first US nationally representative serum 25-hydroxyvitamin D [25(OH)D] concentrations measured by standardized liquid chromatography-tandem mass spectrometry. OBJECTIVE: We describe patterns for total 25(OH)D and individual metabolites in persons aged ≥1 y stratified by race-ethnicity and grouped by demographic, intake, physiologic, and lifestyle variables. METHODS: We measured 25-hydroxycholecalciferol [25(OH)D3], 25-hydroxyergocalciferol [25(OH)D2], and C3-epimer of 25(OH)D3[C3-epi-25(OH)D3] in serum samples (n= 15,652) from the 2007-2010 cross-sectional NHANES [total 25(OH)D = 25(OH)D3+ 25(OH)D2]. RESULTS: Concentrations (median, detection rate) of 25(OH)D3(63.6 nmol/L, 100%) and C3-epi-25(OH)D3(3.40 nmol/L, 86%) were generally detectable; 25(OH)D2was detectable in 19% of the population. Total 25(OH)D, 25(OH)D3, and C3-epi-25(OH)D3displayed similar demographic patterns and were strongly correlated (Spearman'sr> 0.70). Concentrations of 25(OH)D2(90th percentile) were much higher in persons aged ≥60 y (17.3 nmol/L) than in younger age groups (≤4.88 nmol/L). We noted significant race-ethnicity differences in mean total 25(OH)D [non-Hispanic blacks (NHBs), Hispanics, and non-Hispanic whites (NHWs): 46.6, 57.2, and 75.2 nmol/L, respectively] and in the prevalence of total 25(OH)D <30 nmol/L overall (24% of NHBs, 6.4% of Hispanics, and 2.3% of NHWs) as well as stratified by season (winter months: 30% of NHBs, 7.5% of Hispanics, and 3.8% of NHWs; summer months: 17% of NHBs, 4.4% of Hispanics, and 1.6% of NHWs). Persons with higher vitamin D intakes (diet, supplements, or both) and those examined during May-October had significantly higher total 25(OH)D. Significant race-ethnicity interactions in a multiple linear regression model confirmed the necessity of providing race-ethnicity-specific estimates of total 25(OH)D. CONCLUSIONS: Race-ethnicity differences in the prevalence of low total 25(OH)D remained strong even after adjustment for season to account for the NHANES design imbalance between season, latitude, and race-ethnicity. The strong correlation between C3-epi-25(OH)D3and 25(OH)D3may be because the epimer is a metabolite of 25(OH)D3.The presence of 25(OH)D2mainly in older persons is likely a result of high-dose prescription vitamin D2. |
Folate status and concentrations of serum folate forms in the US population: National Health and Nutrition Examination Survey 2011-2
Pfeiffer CM , Sternberg MR , Fazili Z , Lacher DA , Zhang M , Johnson CL , Hamner HC , Bailey RL , Rader JI , Yamini S , Berry RJ , Yetley EA . Br J Nutr 2015 113 (12) 1-13 Serum and erythrocyte (RBC) total folate are indicators of folate status. No nationally representative population data exist for folate forms. We measured the serum folate forms (5-methyltetrahydrofolate (5-methylTHF), unmetabolised folic acid (UMFA), non-methyl folate (sum of tetrahydrofolate (THF), 5-formyltetrahydrofolate (5-formylTHF), 5,10-methenyltetrahydrofolate (5,10-methenylTHF)) and MeFox (5-methylTHF oxidation product)) by HPLC-MS/MS and RBC total folate by microbiologic assay in US population ≥ 1 year (n approximately 7500) participating in the National Health and Nutrition Examination Survey 2011-2. Data analysis for serum total folate was conducted including and excluding MeFox. Concentrations (geometric mean; detection rate) of 5-methylTHF (37.5 nmol/l; 100 %), UMFA (1.21 nmol/l; 99.9 %), MeFox (1.53 nmol/l; 98.8 %), and THF (1.01 nmol/l; 85.2 %) were mostly detectable. 5-FormylTHF (3.6 %) and 5,10-methenylTHF (4.4 %) were rarely detected. The biggest contributor to serum total folate was 5-methylTHF (86.7 %); UMFA (4.0 %), non-methyl folate (4.7 %) and MeFox (4.5 %) contributed smaller amounts. Age was positively related to MeFox, but showed a U-shaped pattern for other folates. We generally noted sex and race/ethnic biomarker differences and weak (Spearman's r< 0.4) but significant (P< 0.05) correlations with physiological and lifestyle variables. Fasting, kidney function, smoking and alcohol intake showed negative associations. BMI and body surface area showed positive associations with MeFox but negative associations with other folates. All biomarkers showed significantly higher concentrations with recent folic acid-containing dietary supplement use. These first-time population data for serum folate forms generally show similar associations with demographic, physiological and lifestyle variables as serum total folate. Patterns observed for MeFox may suggest altered folate metabolism dependent on biological characteristics. |
Unmetabolized folic acid is detected in nearly all serum samples from US children, adolescents, and adults
Pfeiffer CM , Sternberg MR , Fazili Z , Yetley EA , Lacher DA , Bailey RL , Johnson CL . J Nutr 2015 145 (3) 520-31 BACKGROUND: Serum total folate consists mainly of 5-methyltetrahydrofolate (5-methylTHF). Unmetabolized folic acid (UMFA) may occur in persons consuming folic acid-fortified foods or supplements. OBJECTIVES: We describe serum 5-methylTHF and UMFA concentrations in the US population ≥1 y of age by demographic variables and fasting time, stratified by folic acid-containing dietary supplement use. We also evaluate factors associated with UMFA concentrations >1 nmol/L. METHODS: Serum samples from the cross-sectional NHANES 2007-2008 were measured for 5-methylTHF (n = 2734) and UMFA (n = 2707) by HPLC-tandem mass spectrometry. RESULTS: In supplement users compared with nonusers, we found significantly higher geometric mean concentrations of 5-methylTHF (48.4 and 30.7 nmol/L, respectively) and UMFA (1.54 and 0.794 nmol/L, respectively). UMFA concentrations were detectable (>0.3 nmol/L) in >95% of supplement users and nonusers, regardless of demographic or fasting characteristics; concentrations differed significantly by age and fasting time, but not by sex and race-ethnicity, both in supplement users and nonusers. The prevalence of UMFA concentrations >1 nmol/L was 33.2% overall and 21.0% in fasting (≥8 h) adults (≥20 y of age). Using multiple logistic regression analysis, UMFA concentrations >1 nmol/L were associated with being older, non-Hispanic black, nonfasting (<8 h), having smaller body surface area, higher total folic acid intake (diet and supplements), and higher red blood cell folate concentrations. In fasting adults, a decrease in the mean daily alcohol consumption was also associated with increased odds of UMFA concentrations >1 nmol/L. CONCLUSIONS: UMFA detection was nearly ubiquitous, and concentrations >1 nmol/L were largely but not entirely explained by fasting status and by total folic acid intake from diet and supplements. These new UMFA data in US persons ≥1 y of age provide much-needed information on this vitamer in a fortified population with relatively high use of dietary supplements. |
Urine sodium excretion increased slightly among U.S. adults between 1988 and 2010
Pfeiffer CM , Hughes JP , Cogswell ME , Burt VL , Lacher DA , Lavoie DJ , Rabinowitz DJ , Johnson CL , Pirkle JL . J Nutr 2014 144 (5) 698-705 Little information is available on temporal trends in sodium intake in the U.S. population using urine sodium excretion as a biomarker. Our aim was to assess 1988-2010 trends in estimated 24-h urine sodium (24hUNa) excretion among U.S. adults (age 20-59 y) participating in the cross-sectional NHANES. We used subsamples from a 1988-1994 convenience sample, a 2003-2006 one-third random sample, and a 2010 one-third random sample to comply with resource constraints. We estimated 24hUNa excretion from measured sodium concentrations in spot urine samples by use of calibration equations (for men and women) derived from the International Cooperative Study on Salt, Other Factors, and Blood Pressure study. Estimated 24hUNa excretion increased over the 20-y period [1988-1994, 2003-2006, and 2010; means +/- SEMs (n): 3160 +/- 38.4 mg/d (1249), 3290 +/- 29.4 mg/d (1235), and 3290 +/- 44.4 mg/d (525), respectively; P-trend = 0.022]. We observed significantly higher mean estimated 24hUNa excretion in each survey period (P < 0.001) for men compared with women (31-33%) and for persons with a higher body mass index (BMI; 32-35% for obese vs. normal weight) or blood pressure (17-26% for hypertensive vs. normal blood pressure). After adjusting for age, sex, and race-ethnicity, temporal trends in mean estimated 24hUNa excretion remained significant (P-trend = 0.004). We observed no temporal trends in mean estimated 24hUNa excretion among BMI subgroups, nor after adjusting for BMI. Although several limitations apply to this analysis (the use of a convenience sample in 1988-1994 and using estimated 24hUNa excretion as a biomarker of sodium intake), these first NHANES data suggest that mean estimated 24hUNa excretion increased slightly in U.S. adults over the past 2 decades, and this increase may be explained by a shift in the distribution of BMI. |
Summary of an NIH workshop to identify research needs to improve the monitoring of iodine status in the United States and to inform the DRI
Swanson CA , Zimmermann MB , Skeaff S , Pearce EN , Dwyer JT , Trumbo PR , Zehaluk C , Andrews KW , Carriquiry A , Caldwell KL , Egan SK , Long SE , Bailey RL , Sullivan KM , Holden JM , Betz JM , Phinney KW , Brooks SP , Johnson CL , Haggans CJ . J Nutr 2012 142 (6) 1175S-85S The Office of Dietary Supplements (ODS) at the NIH sponsored a workshop on May 12-13, 2011, to bring together representatives from various NIH institutes and centers as a first step in developing an NIH iodine research initiative. The workshop also provided an opportunity to identify research needs that would inform the dietary reference intakes for iodine, which were last revised in 2001. Iodine is required throughout the life cycle, but pregnant women and infants are the populations most at risk of deficiency, because iodine is required for normal brain development and growth. The CDC monitors iodine status of the population on a regular basis, but the status of the most vulnerable populations remains uncertain. The NIH funds very little investigator-initiated research relevant to iodine and human nutrition, but the ODS has worked for several years with a number of other U.S. government agencies to develop many of the resources needed to conduct iodine research of high quality (e.g., validated analytical methods and reference materials for multiple types of samples). Iodine experts, scientists from several U.S. government agencies, and NIH representatives met for 2 d to identify iodine research needs appropriate to the NIH mission. |
Estimation of trends in serum and RBC folate in the U.S. population from pre- to postfortification using assay-adjusted data from the NHANES 1988-2010
Pfeiffer CM , Hughes JP , Lacher DA , Bailey RL , Berry RJ , Zhang M , Yetley EA , Rader JI , Sempos CT , Johnson CL . J Nutr 2012 142 (5) 886-93 The NHANES has monitored folate status of the U.S. population from prefortification (1988-1994) to postfortification (1999-2010) by measuring serum and RBC folate concentrations. The Bio-Rad radioassay (BR) was used from 1988 to 2006, and the microbiologic assay (MBA) was used from 2007 to 2010. The MBA produces higher concentrations than the BR and is considered to be more accurate. Thus, to bridge assay differences and to examine folate trends over time, we adjusted the BR results to be comparable to the MBA results. Postfortification, assay-adjusted serum and RBC folate concentrations were 2.5 times and 1.5 times prefortification concentrations, respectively, and showed a significant linear trend (P < 0.001) to slightly lower concentrations during 1999-2010. The postfortification prevalence of low serum (<10 nmol/L) or RBC (<340 nmol/L) folate concentrations was ≤ 1%, regardless of demographic subgroup, compared with 24% for serum folate and 3.5% for RBC folate prefortification, with substantial variation among demographic subgroups. The central 95% reference intervals for serum and RBC folate varied by demographic subgroup during both pre- and postfortification periods. Age and dietary supplement use had the greatest effects on prevalence estimates of low folate concentrations during the prefortification period. In summary, the MBA-equivalent blood folate concentrations in the U.S. population showed first a sharp increase from pre- to postfortification, then showed a slight decrease (17% for serum and 12% for RBC folate) during the 12-y postfortification period. The MBA-equivalent pre- and postfortification reference concentrations will inform countries that plan folic acid fortification or that need to evaluate its impact. |
Assessing vitamin status in large population surveys by measuring biomarkers and dietary intake - two case studies: folate and vitamin D
Pfeiffer CM , Schleicher RL , Johnson CL , Coates PM . Food Nutr Res 2012 56 The National Health and Nutrition Examination Survey (NHANES) provides the most comprehensive assessment of the health and nutrition status of the US population. Up-to-date reference intervals on biomarkers and dietary intake inform the scientific and public health policy communities on current status and trends over time.The main purpose of dietary assessment methods such as the food-frequency questionnaire, food record (or diary), and 24-hr dietary recall is to estimate intake of nutrients and, together with supplement usage information, describe total intake of various foods or nutrients. As with all self-reporting methods, these tools are challenging to use and interpret. Yet, they are needed to establish dietary reference intake recommendations and to evaluate what proportion of the population meets these recommendations. While biomarkers are generally expensive and, to some degree, invasive, there is no question as to their ability to assess nutrition status. In some cases biomarkers can also be used to assess intake or function, although rarely can one biomarker fulfill all these purposes. For example, serum folate is a good indicator of folate intake, red blood cell (RBC) folate is a good status indicator, and plasma total homocysteine is a good functional indicator of one-carbon metabolism. Using folate and vitamin D - two vitamins that are currently hotly debated in the public health arena - as two case studies, we discuss the complexities of using biomarkers and total intake information to assess nutrition status. These two examples also show how biomarkers and intake provide different information and how both are needed to evaluate and set public health policy. We also provide guidance on general requirements for using nutrition biomarkers and food and supplement intake information in longitudinal, population-based surveys. |
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
Pfeiffer CM , Hughes JP , Durazo-Arvizu RA , Lacher DA , Sempos CT , Zhang M , Yetley EA , Johnson CL . J Nutr 2012 142 (5) 894-900 The NHANES measured serum and RBC folate concentrations by using a radioassay during prefortification (1988-1994) and postfortification (1999-2006) periods followed by the use of a microbiologic assay (MBA) from 2007-2010. The MBA produces higher concentrations than does the radioassay and is considered to be more accurate. To allow for accurate long-term trending (1988-2010), we evaluated different regression models (linear, piecewise linear, and fractional polynomial) to assay-adjust the radioassay results to be comparable to the MBA results. The data used to derive the regression models originated from 2 crossover studies in which the 2 assays were applied to a set of 325 serum and 171 whole-blood samples. Fractional polynomial regression of logarithmically transformed data provided the best fit for serum folate. Linear regression of logarithmically transformed whole-blood data provided an equally good fit compared with the other models and was the simplest to apply for RBC folate. Prefortification serum and RBC folate geometric mean concentrations increased after adjustment from 13.0 to 16.7 nmol/L and from 403 to 747 nmol/L, respectively. Postfortification serum folate concentrations increased from ~30 to ~43 nmol/L, and RBC folate concentrations increased from ~600 to ~1100 nmol/L after adjustment, with some variation across survey cycles. The presented regression equations allow the estimation of more accurate prevalence estimates and long-term trends in blood folate concentrations in the U.S. population by using results that are equivalent to the MBA. This information will be useful to public health officials in the United States who are dealing with folic acid fortification issues. |
Levels of plasma trans-fatty acids in non-Hispanic white adults in the United States in 2000 and 2009
Vesper HW , Kuiper HC , Mirel LB , Johnson CL , Pirkle JL . JAMA 2012 307 (6) 562-3 Levels of trans-fatty acids (TFAs) in blood come from natural sources, such as milk, and industrial sources, such as partially hydrogenated vegetable oils. Dietary intake of TFAs increases low-density lipoprotein cholesterol (LDL-C) and has other adverse metabolic effects.1 Changing to a diet low in TFAs may lower the LDL-C level and decrease the risk for cardiovascular disease. To assist consumers, the Food and Drug Administration amended its regulations in 2003 to require that TFA content be declared on the nutrition label of foods and dietary supplements.2 Some community and state health departments have required restaurants to limit TFAs and reductions have been shown in supermarket and restaurant products. | The public health impact of these changes on TFA blood levels in the population is unknown. A preliminary study was conducted to determine plasma concentrations of TFAs in a subset of non-Hispanic white adults in the National Health and Nutrition Examination Survey (NHANES) in 2000 and 2009. |
Folate and vitamin B-12 biomarkers in NHANES: history of their measurement and use
Yetley EA , Johnson CL . Am J Clin Nutr 2011 94 (1) 322S-31S NHANES measured folate and vitamin B-12 status biomarkers, starting with serum folate from NHANES I (1974-1975) through 2010. Subsequent NHANES measured additional biomarkers [eg, red blood cell folate, serum vitamin B-12, total homocysteine (tHcy), methylmalonic acid, serum folic acid, and 5-methyltetrahydrofolic acid]. Examples of the uses of these data are wide ranging and include public policy applications, the derivation of reference intervals, and research. Periodically, the National Center for Health Statistics and its federal partners convene expert panels to review the use of the folate- and vitamin B-12-related biomarkers in NHANES. These panels have evaluated the need for results to be comparable across time and with published data and the use of crossover studies and adjustment equations to ensure comparability. With the recent availability of reference methods and materials for serum folate and tHcy, NHANES has started to use traceability approaches to enhance the accuracy and comparability of its results. A major user concern over the years has been the use of cutoffs to estimate the prevalence of inadequate folate and vitamin B-12 status. Because these cutoffs depend on the measurement procedure, several expert panels suggested approaches for dealing with cutoff challenges. This review summarizes the history and use of folate- and vitamin B-12-related biomarkers beginning with NHANES I (1974-1975) through 2010. |
Comparison of serum and red blood cell folate microbiologic assays for national population surveys
Pfeiffer CM , Zhang M , Lacher DA , Molloy AM , Tamura T , Yetley EA , Picciano MF , Johnson CL . J Nutr 2011 141 (7) 1402-9 Three laboratories participated with their laboratory-specific microbiologic growth assays (MA) in the NHANES 2007-2008 to assess whether the distributions of serum (n = 2645) and RBC folate (n = 2613) for the same one-third sample of participants were comparable among laboratories. Laboratory (L) 2 produced the highest and L1 the lowest serum and RBC folate geometric means (nmol/L) in the NHANES sample (serum: L1, 39.5; L2, 59.2; L3, 47.7; and RBC: L1, 1120; L2, 1380; L3, 1380). Each laboratory produced different reference intervals for the central 95% of the population. Pearson correlation coefficients were highest between L3 and L1 (serum, r = 0.95; RBC, r = 0.92) and lowest between L2 and L1 (serum, r = 0.81; RBC, r = 0.65). Notable procedural differences among the laboratories were the Lactobacillus rhamnosus microorganism (L1 and L3: chloramphenicol resistant, L2: wild type) and the calibrator [L1: [6S]5-methyltetrahydrofolate (5-methylTHF), L2: [6R,S] 5-formyltetrahydrofolate ([6R,S] 5-formylTHF), L3: folic acid (FA)]. Compared with 5-methylTHF as calibrator, the folate results were 22-32% higher with FA as calibrator and 8% higher with 5-formylTHF as calibrator, regardless of the matrix (n = 30 serum, n = 28 RBC). The use of different calibrators explained most of the differences in results between L3 and L1 but not between L2 and L1. The use of the wild-type L. rhamnosus by L2 appeared to be the main reason for the differences in results between L2 and the other 2 laboratories. These findings indicate how assay variations influence MA folate results and how those variations can affect population data. To ensure data comparability, better assay harmonization is needed. |
Overview of a roundtable on NHANES monitoring of biomarkers of folate and vitamin B-12 status: measurement procedure issues
Yetley EA , Coates PM , Johnson CL . Am J Clin Nutr 2011 94 (1) 297S-302S A roundtable dialogue to discuss "NHANES Monitoring of Biomarkers of Folate and Vitamin B-12 Status" took place in July 2010. This article provides an overview of the meeting and this supplement issue. Although the focus of the roundtable dialogue was on the measurement of folate and vitamin B-12 status biomarkers in the NHANES, this article also describes the relevance and importance of these issues for clinical and research laboratories. The roundtable identified the microbiological assay (MA) as the gold standard for measurement of serum and red blood cell folate concentrations. The roundtable noted that differences in results between the Bio-Rad Quantaphase II procedure (Bio-Rad Laboratories, Hercules, CA) that NHANES 1991-1994 and 1999-2006 used and the MA that NHANES 2007-2010 used will require adjustment equations to evaluate time trends. The roundtable found that the close agreement between the serum results for the MA and liquid chromatography-tandem mass spectrometry (LC-MS/MS) procedures supported the conversion to LC-MS/MS for serum folate in future NHANES. The roundtable recognized the uncertainty about whether subclinical vitamin B-12 deficiency is a public health concern but encouraged reinstatement of at least one circulating vitamin B-12 measure and one functional vitamin B-12 status measure in future NHANES. The use of serum vitamin B-12 and plasma methylmalonic acid would provide continuity with past NHANES. The roundtable supported the continued use of the National Institute of Standards and Technology (NIST) reference materials in NHANES biomarker analyses and the further development of additional reference materials by the NIST. |
Biomarkers of folate status in NHANES: a roundtable summary
Yetley EA , Pfeiffer CM , Phinney KW , Fazili Z , Lacher DA , Bailey RL , Blackmore S , Bock JL , Brody LC , Carmel R , Curtin LR , Durazo-Arvizu RA , Eckfeldt JH , Green R , Gregory JF 3rd , Hoofnagle AN , Jacobsen DW , Jacques PF , Molloy AM , Massaro J , Mills JL , Nexo E , Rader JI , Selhub J , Sempos C , Shane B , Stabler S , Stover P , Tamura T , Tedstone A , Thorpe SJ , Coates PM , Johnson CL , Picciano MF . Am J Clin Nutr 2011 94 (1) 303S-312S A roundtable to discuss the measurement of folate status biomarkers in NHANES took place in July 2010. NHANES has measured serum folate since 1974 and red blood cell (RBC) folate since 1978 with the use of several different measurement procedures. Data on serum 5-methyltetrahydrofolate (5MTHF) and folic acid (FA) concentrations in persons aged ≥60 y are available in NHANES 1999-2002. The roundtable reviewed data that showed that folate concentrations from the Bio-Rad Quantaphase II procedure (Bio-Rad Laboratories, Hercules, CA; used in NHANES 1991-1994 and NHANES 1999-2006) were, on average, 29% lower for serum and 45% lower for RBC than were those from the microbiological assay (MA), which was used in NHANES 2007-2010. Roundtable experts agreed that these differences required a data adjustment for time-trend analyses. The roundtable reviewed the possible use of an isotope-dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) measurement procedure for future NHANES and agreed that the close agreement between the MA and LC-MS/MS results for serum folate supported conversion to the LC-MS/MS procedure. However, for RBC folate, the MA gave 25% higher concentrations than did the LC-MS/MS procedure. The roundtable agreed that the use of the LC-MS/MS procedure to measure RBC folate is premature at this time. The roundtable reviewed the reference materials available or under development at the National Institute of Standards and Technology and recognized the challenges related to, and the scientific need for, these materials. They noted the need for a commutability study for the available reference materials for serum 5MTHF and FA. |
Cholesterol management in the United States: the National Health and Nutrition Examination Survey, 1999 to 2006
Yoon SS , Carroll MD , Johnson CL , Gu Q . Ann Epidemiol 2011 21 (5) 318-26 OBJECTIVES: This study assesses (1) the prevalence of ever having a blood test for cholesterol, (2) current practices of following advice from a health care professional to manage high cholesterol, and (3) the association between total serum cholesterol level and following the advice. METHODS: A total of 17,260 adults aged 20 and older participated in the interview and medical examination in National Health and Nutrition Examination Survey (1999-2006). Cholesterol management was examined among adults previously diagnosed with high cholesterol who were advised to change their lifestyles through low-fat diets, weight loss, or exercise and/or to take medications. Five analytic groups were defined: (1) Those taking medications only, (2) those making one or more lifestyle changes, (3) those making one or two lifestyle changes and taking medications, (4) those making three lifestyle changes and taking medications, and (5) those not following any advice. RESULTS: Between 69% and 80% of adults advised to lower cholesterol reported following advice to control their cholesterol. Adults on medication only and adults with lifestyle changes and medication were more likely to have cholesterol level below 240 mg/dL compared with adults with lifestyle changes only (medication only: odds ratio [OR], 2.7; 95% confidence interval [CI], 1.3-5.8); one or two lifestyle changes and medication: OR, 4.1; 95% CI, 3.1-5.4; three lifestyle changes and medication: OR, 4.3; 95% CI, 3.0-6.2; referent: one or two or three lifestyle changes). CONCLUSION: The combination of medication and lifestyle changes was more strongly associated with decreasing cholesterol compared with making one or more lifestyle changes without medication use. |
Multiple imputation of missing dual-energy X-ray absorptiometry data in the National Health and Nutrition Examination Survey
Schenker N , Borrud LG , Burt VL , Curtin LR , Flegal KM , Hughes J , Johnson CL , Looker AC , Mirel L . Stat Med 2010 30 (3) 260-76 In 1999, dual-energy x-ray absorptiometry (DXA) scans were added to the National Health and Nutrition Examination Survey (NHANES) to provide information on soft tissue composition and bone mineral content. However, in 1999-2004, DXA data were missing in whole or in part for about 21 per cent of the NHANES participants eligible for the DXA examination; and the missingness is associated with important characteristics such as body mass index and age. To handle this missing-data problem, multiple imputation of the missing DXA data was performed. Several features made the project interesting and challenging statistically, including the relationship between missingness on the DXA measures and the values of other variables; the highly multivariate nature of the variables being imputed; the need to transform the DXA variables during the imputation process; the desire to use a large number of non-DXA predictors, many of which had small amounts of missing data themselves, in the imputation models; the use of lower bounds in the imputation procedure; and relationships between the DXA variables and other variables, which helped both in creating and evaluating the imputations. This paper describes the imputation models, methods, and evaluations for this publicly available data resource and demonstrates properties of the imputations via examples of analyses of the data. The analyses suggest that imputation helps to correct biases that occur in estimates based on the data without imputation, and that it helps to increase the precision of estimates as well. Moreover, multiple imputation usually yields larger estimated standard errors than those obtained with single imputation. Published in 2010 by John Wiley & Sons, Ltd. |
NHANES monitoring of serum 25-hydroxyvitamin D: a roundtable summary
Yetley EA , Pfeiffer CM , Schleicher RL , Phinney KW , Lacher DA , Christakos S , Eckfeldt JH , Fleet JC , Howard G , Hoofnagle AN , Hui SL , Lensmeyer GL , Massaro J , Peacock M , Rosner B , Wiebe D , Bailey RL , Coates PM , Looker AC , Sempos C , Johnson CL , Picciano MF . J Nutr 2010 140 (11) 2030S-45S A roundtable to discuss monitoring of serum 25-hydroxyvitamin D [25(OH)D] in the NHANES was held in late July 2009. Topics included the following: 1) options for dealing with assay fluctuations in serum 25(OH)D in the NHANES conducted between 1988 and 2006; 2) approaches for transitioning between the RIA used in the NHANES between 1988 and 2006 to the liquid chromatography tandem MS (LC-MS/MS) measurement procedure to be used in NHANES 2007 and later; 3) approaches for integrating the recently available standard reference material for vitamin D in human serum (SRM 972) from the National Institute of Standards and Technology (NIST) into the NHANES; 4) questions regarding whether the C-3 epimer of 25-hydroxyvitamin D3 [3-epi-25(OH)D3] should be measured in NHANES 2007 and later; and 5) identification of research and educational needs. The roundtable experts agreed that the NHANES data needed to be adjusted to control for assay fluctuations and offered several options for addressing this issue. The experts suggested that the LC-MS/MS measurement procedure developed by NIST could serve as a higher order reference measurement procedure. They noted the need for a commutability study for the recently released NIST SRM 972 across a range of measurement procedures. They suggested that federal agencies and professional organizations work with manufacturers to improve the quality and comparability of measurement procedures across all laboratories. The experts noted the preliminary nature of the evidence of the 3-epi-25(OH)D3 but felt that it should be measured in 2007 NHANES and later. |
Characterizing extreme values of body mass index for age by using the 2000 Centers for Disease Control and Prevention growth charts
Flegal KM , Wei R , Ogden CL , Freedman DS , Johnson CL , Curtin LR . Am J Clin Nutr 2009 90 (5) 1314-20 BACKGROUND: The 2000 Centers for Disease Control and Prevention (CDC) growth charts included lambda-mu-sigma (LMS) parameters intended to calculate smoothed percentiles from only the 3rd to the 97th percentile. OBJECTIVE: The objective was to evaluate different approaches to describing more extreme values of BMI-for-age by using simple functions of the CDC growth charts. DESIGN: Empirical data for the 99th and the 1st percentiles of body mass index (BMI)-for-age were calculated from the data set used to construct the growth charts and were compared with estimates extrapolated from the CDC-supplied LMS parameters and to various functions of other smoothed percentiles. A set of reestimated LMS parameters that incorporated a smoothed 99th percentile were also evaluated. RESULTS: Extreme percentiles extrapolated from the CDC-supplied LMS parameters did not match well to the empirical data for the 99th percentile. A better fit to the empirical data was obtained by using 120% of the smoothed 95th percentile. The empirical first percentile was reasonably well approximated by extrapolations from the LMS values. The reestimated LMS parameters had several drawbacks and no clear advantages. CONCLUSIONS: Several approximations can be used to describe extreme high values of BMI-for-age with the use of the CDC growth charts. Extrapolation from the CDC-supplied LMS parameters does not provide a good fit to the empirical 99th percentile values. Simple approximations to high values as percentages of the existing smoothed percentiles have some practical advantages over imputation of very high percentiles. The expression of high BMI values as a percentage of the 95th percentile can provide a flexible approach to describing and tracking heavier children. |
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