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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

UFR (mL/hr) (A) and UFRBW (mL/hr-kg) (B) as a function of age in the NHANES 2009–2012 data sets. Blue line is the fractional polynomial fit with 95% CI to the logarithm of urinary flow rate vs. age.
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f1: UFR (mL/hr) (A) and UFRBW (mL/hr-kg) (B) as a function of age in the NHANES 2009–2012 data sets. Blue line is the fractional polynomial fit with 95% CI to the logarithm of urinary flow rate vs. age.

Mentions: UFR data were available for 14,631 participants in the 2009–2012 NHANES cycles. Summary statistics on the distributions of collected void volumes and time covered by the collected urine samples by age group are presented in Table 1. The GMs for UFR and UFRBW across the entire 2009–2012 NHANES data set were 47.76 mL/hr (95% CI: 45.64, 49.98 mL/hr) and 0.65 mL/hr-kg (95% CI: 0.63, 0.67 mL/hr-kg), respectively. Patterns of UFR and UFRBW with age were assessed visually and notable differences among age groups were observed (Figure 1). UFR as a function of age rises through childhood and into adulthood and then declines in older adults. UFRBW exhibits a steep decline in children < 12 years of age, with a more gradual decline with age after 12 years. As a result, subsequent assessments relied upon age stratification.


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)

UFR (mL/hr) (A) and UFRBW (mL/hr-kg) (B) as a function of age in the NHANES 2009–2012 data sets. Blue line is the fractional polynomial fit with 95% CI to the logarithm of urinary flow rate vs. age.
© Copyright Policy - public-domain
Related In: Results  -  Collection

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

f1: UFR (mL/hr) (A) and UFRBW (mL/hr-kg) (B) as a function of age in the NHANES 2009–2012 data sets. Blue line is the fractional polynomial fit with 95% CI to the logarithm of urinary flow rate vs. age.
Mentions: UFR data were available for 14,631 participants in the 2009–2012 NHANES cycles. Summary statistics on the distributions of collected void volumes and time covered by the collected urine samples by age group are presented in Table 1. The GMs for UFR and UFRBW across the entire 2009–2012 NHANES data set were 47.76 mL/hr (95% CI: 45.64, 49.98 mL/hr) and 0.65 mL/hr-kg (95% CI: 0.63, 0.67 mL/hr-kg), respectively. Patterns of UFR and UFRBW with age were assessed visually and notable differences among age groups were observed (Figure 1). UFR as a function of age rises through childhood and into adulthood and then declines in older adults. UFRBW exhibits a steep decline in children < 12 years of age, with a more gradual decline with age after 12 years. As a result, subsequent assessments relied upon age stratification.

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