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Variation in urinary flow rates according to demographic characteristics and body mass index in NHANES: potential confounding of associations between health outcomes and urinary biomarker concentrations.

Hays SM, Aylward LL, Blount BC - Environ. Health Perspect. (2015)

Bottom Line: UFR, but not UFRBW, differed significantly by sex (males > females after age 12 years).Conventional hydration status adjustments did not fully address the effect of flow rate variations.These variations can confound assessments of potential exposure-health outcome associations based on urinary concentration.

View Article: PubMed Central - PubMed

Affiliation: Summit Toxicology, LLP, Lyons, Colorado, USA.

ABSTRACT

Background: Urinary analyte concentrations are affected both by exposure level and by urinary flow rate (UFR). Systematic variations in UFR with demographic characteristics or body mass index (BMI) could confound assessment of associations between health outcomes and biomarker concentrations.

Objectives: We assessed patterns of UFR (milliliters per hour) and body weight-adjusted UFR (UFRBW; milliliters per kilogram per hour) across age, sex, race/ethnicity, and BMI category in the NHANES (National Health and Nutrition Examination Survey) 2009-2012 data sets.

Methods: Geometric mean (GM) UFR and UFRBW were compared across age-stratified (6-11, 12-19, 20-39, 40-59, and ≥ 60 years) subgroups (sex, race/ethnicity, and BMI category). Patterns of analyte urinary concentration or mass excretion rates (nanograms per hour and nanograms per kilogram per hour BW) were assessed in sample age groups for case study chemicals bisphenol A and 2,5-dichlorophenol.

Results: UFR increased from ages 6 to 60 years and then declined with increasing age. UFRBW varied inversely with age. UFR, but not UFRBW, differed significantly by sex (males > females after age 12 years). Differences in both metrics were observed among categories of race/ethnicity. UFRBW, but not UFR, varied inversely with BMI category and waist circumference in all age groups. Urinary osmolality increased with increasing BMI. Case studies demonstrated different exposure-outcome relationships depending on exposure metric. Conventional hydration status adjustments did not fully address the effect of flow rate variations.

Conclusions: UFR and UFRBW exhibit systematic variations with age, sex, race/ethnicity, and BMI category. These variations can confound assessments of potential exposure-health outcome associations based on urinary concentration. Analyte excretion rates are valuable exposure metrics in such assessments.

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Related in: MedlinePlus

GM (95% CI) urinary 25DCP concentration, creatinine-adjusted concentration, osmolality-adjusted concentration, and mass excretion rates [(ng/hr)/100 or ng/hr-kg] by BMI category in children and adolescents in the NHANES 2009–2012 data sets. Mass excretion rates were plotted divided by 100 to allow comparison of pattern on the same numerical scale with the other metrics.p-Values are assessment for trend across BMI categories.
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f4: GM (95% CI) urinary 25DCP concentration, creatinine-adjusted concentration, osmolality-adjusted concentration, and mass excretion rates [(ng/hr)/100 or ng/hr-kg] by BMI category in children and adolescents in the NHANES 2009–2012 data sets. Mass excretion rates were plotted divided by 100 to allow comparison of pattern on the same numerical scale with the other metrics.p-Values are assessment for trend across BMI categories.

Mentions: 25DCP and BMI in children and adolescents. GM urinary concentrations of 25DCP in children and adolescents also trended upward with BMI category, doubling between the lowest and highest BMI categories (Figure 4). After applying hydration status adjustment using creatinine, the trend became nonsignificant. The trend remained when osmolality adjustment was applied. GM mass excretion rates (nanograms per hour) showed a similar pattern to that for unadjusted concentration, whereas there was no trend in body weight–adjusted excretion rates across BMI categories.


Variation in urinary flow rates according to demographic characteristics and body mass index in NHANES: potential confounding of associations between health outcomes and urinary biomarker concentrations.

Hays SM, Aylward LL, Blount BC - Environ. Health Perspect. (2015)

GM (95% CI) urinary 25DCP concentration, creatinine-adjusted concentration, osmolality-adjusted concentration, and mass excretion rates [(ng/hr)/100 or ng/hr-kg] by BMI category in children and adolescents in the NHANES 2009–2012 data sets. Mass excretion rates were plotted divided by 100 to allow comparison of pattern on the same numerical scale with the other metrics.p-Values are assessment for trend across BMI categories.
© Copyright Policy - public-domain
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384205&req=5

f4: GM (95% CI) urinary 25DCP concentration, creatinine-adjusted concentration, osmolality-adjusted concentration, and mass excretion rates [(ng/hr)/100 or ng/hr-kg] by BMI category in children and adolescents in the NHANES 2009–2012 data sets. Mass excretion rates were plotted divided by 100 to allow comparison of pattern on the same numerical scale with the other metrics.p-Values are assessment for trend across BMI categories.
Mentions: 25DCP and BMI in children and adolescents. GM urinary concentrations of 25DCP in children and adolescents also trended upward with BMI category, doubling between the lowest and highest BMI categories (Figure 4). After applying hydration status adjustment using creatinine, the trend became nonsignificant. The trend remained when osmolality adjustment was applied. GM mass excretion rates (nanograms per hour) showed a similar pattern to that for unadjusted concentration, whereas there was no trend in body weight–adjusted excretion rates across BMI categories.

Bottom Line: UFR, but not UFRBW, differed significantly by sex (males > females after age 12 years).Conventional hydration status adjustments did not fully address the effect of flow rate variations.These variations can confound assessments of potential exposure-health outcome associations based on urinary concentration.

View Article: PubMed Central - PubMed

Affiliation: Summit Toxicology, LLP, Lyons, Colorado, USA.

ABSTRACT

Background: Urinary analyte concentrations are affected both by exposure level and by urinary flow rate (UFR). Systematic variations in UFR with demographic characteristics or body mass index (BMI) could confound assessment of associations between health outcomes and biomarker concentrations.

Objectives: We assessed patterns of UFR (milliliters per hour) and body weight-adjusted UFR (UFRBW; milliliters per kilogram per hour) across age, sex, race/ethnicity, and BMI category in the NHANES (National Health and Nutrition Examination Survey) 2009-2012 data sets.

Methods: Geometric mean (GM) UFR and UFRBW were compared across age-stratified (6-11, 12-19, 20-39, 40-59, and ≥ 60 years) subgroups (sex, race/ethnicity, and BMI category). Patterns of analyte urinary concentration or mass excretion rates (nanograms per hour and nanograms per kilogram per hour BW) were assessed in sample age groups for case study chemicals bisphenol A and 2,5-dichlorophenol.

Results: UFR increased from ages 6 to 60 years and then declined with increasing age. UFRBW varied inversely with age. UFR, but not UFRBW, differed significantly by sex (males > females after age 12 years). Differences in both metrics were observed among categories of race/ethnicity. UFRBW, but not UFR, varied inversely with BMI category and waist circumference in all age groups. Urinary osmolality increased with increasing BMI. Case studies demonstrated different exposure-outcome relationships depending on exposure metric. Conventional hydration status adjustments did not fully address the effect of flow rate variations.

Conclusions: UFR and UFRBW exhibit systematic variations with age, sex, race/ethnicity, and BMI category. These variations can confound assessments of potential exposure-health outcome associations based on urinary concentration. Analyte excretion rates are valuable exposure metrics in such assessments.

Show MeSH
Related in: MedlinePlus