The role of age and sex in non-linear dilution adjustment of spot urine arsenic

Abstract

Background: Previous research introduced V-PFCRC as an effective spot urinary dilution adjustment method for various metal analytes, including the major environmental toxin arsenic. V-PFCRC normalizes analytes to 1 g/L creatinine (CRN) by adopting more advanced power-functional corrective equations accounting for variation in exposure level. This study expands on previous work by examining the impacts of age and sex on corrective functions.

Methods: Literature review of the effects of sex and age on urinary dilution and the excretion of CRN and arsenic. Data analysis included a Data Set 1 of 5,752 urine samples and a partly overlapping Data Set 2 of 1,154 combined EDTA blood and urine samples. Both sets were classified into age bands, and the means, medians, and interquartile ranges for CRN and TWuAs in uncorrected (UC), conventionally CRN-corrected (CCRC), simple power-functional (S-PFCRC), sex-aggregated (V-PFCRC SA), and sex-differentiated V-PFCRC SD modes were compared. Correlation analyses assessed residual relationships between CRN, TWuAs, and age. V-PFCRC functions were compared across three numerically similar age groups and both sexes. The efficacy of systemic dilution adjustment error compensation was evaluated through power-functional regression analysis of residual CRN and the association between arsenic in blood and all tested urinary result modes.

Results: Significant sex differences in UC and blood were neutralized by CCRC and reduced by V-PFCRC. Age showed a positive association with blood arsenic and TWuAs in all result modes, indicating factual increments in exposure. Sex-differentiated V-PFCRC best matched the sex-age kinetics of blood arsenic. V-PFCRC formulas varied by sex and age and appeared to reflect urinary osmolality sex-age-kinetics reported in previous research. V-PFCRC minimized residual biases of CRN on TWuAs across all age groups and sexes, demonstrating improved standardization efficacy compared to UC and CCRC arsenic.

Interpretation: Sex differences in UC and CCRC arsenic are primarily attributable to urinary dilution and are effectively compensated by V-PFCRC. While the sex and age influence on V-PFCRC formulas align with sex- and age-specific urinary osmolality and assumed baseline vasopressor activities, their impact on correction validity for entire collectives is minimal.

Conclusion: The V-PFCRC method offers a robust correction for urinary arsenic dilution, significantly reducing systemic dilution adjustment errors. Its application in various demographic contexts enhances the accuracy of urinary biomarker assessments, benefiting clinical and epidemiological research. V-PFCRC effectively compensates for sex differences in urinary arsenic. Age-related increases in TWuAs are exposure-related and should be additionally accounted for by algebraic normalization, covariate models, or standard range adjustments.

Keywords: Arsenic; Biomarkers; Exposure studies; Non-linear dilution adjustment; Sex-age differences; Spot urine.

Fig. 1

Sex-Differentiated Influence of Age on CRN and Urinary Arsenic across five result modes in Set 1. Means ± standard errors are plotted for nine 10-year age bands. Outliers above the 95% and below the 5% percentile of each age band were not analyzed. Post-outlier exclusion sample sizes are listed in Graph A. Urinary result modes are detailed in Table 3. Group statistics are provided in the Supplementary Excel file. Significance levels of sex differences (2-sided t-test): * 0.05 ≥ p > 0.025, ** 0.025 ≥ p > 0.01, *** p < 0.001

Fig. 2

Sex-Differentiated Influence of Age on CRN, Urine, and Blood Arsenic in Set 2. Analogous representation to Fig. 1 for Data Set 2, including arsenic values in EDTA blood determined in parallel with urine of three result modes in four 15-year-age bands (21–35, 36–50, 51–65, and 66–80 years). Means ± standard errors for the remaining 486 female and 476 male samples are plotted. Significance level of sex-difference (2-sided t-tests): * 0.05 > p > 0.025, ** 0.025 ≥ p > 0.01, *** p < 0.001

Fig. 3

Comparison of Age Effects on Arsenic Concentrations in Blood and Urine. Percentage deviations of medians and quartile (Q1 and Q3) limits of the three older age groups of Set 2 (36–50,51–65, and 66–80) from the youngest age group (21–35 years) are plotted for blood and urine in UC, CCRC, and V-PFCRC mode

Fig. 4

Sex-Ratios of Quartile Limits for CRN, Blood- and Urine Arsenic

Fig. 5

Percentual deviations of urinary from blood sex ratios of Arsenic Quartiles 1–3. The Female/Male ratios of arsenic quartiles 1–3 for urine in UC, CCRC, and V-PFCRC mode were divided by those for blood. The percentual deviation was calculated as shown in the abscissa labeling. Values less than 0 indicate a higher female/male blood ratio than urine and vice versa. The smaller the deviation from zero, the higher the agreement between blood and urine

Fig. 6

Age- and Sex-differentiated log-linear relationships between Exponents b and V-PFCRC normalized arsenic to 1 g/L CRN. Curves are sorted by either sex (A) or age group (B)

Fig. 7

Sex- and age-differentiated efficacy of standardization determined by residual dependence of Arsenic on CRN in various age and sex groups of Set 1. Residual dependence was analyzed based on slopes and R2 of power-functional regression analysis of each subset

Fig. 8

Sex- and age-differentiated associations between blood and urine arsenic in Set 2 subgroups. Dependence was analyzed based on R² of power-functional regression analysis of each subset

Fig. 9

Dilution-dependent result fluctuations of arsenic in uncorrected, conventional, and variable power-functionally corrected result mode