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To address the data gap, we conducted this study in 11 men with the intention to a) assess the reproducibility of serial measurements of As, Cd, Co, Cu, Mo, Ni, and Pb in urine during a 3-month period; b) assess the effect of concentration corrections, including creatinine correction, creatinine as a covariate, and the urinary excretion rate (UER) calculation, on the reproducibility of metal measurements; c) evaluate the correlation between spot, first morning, and 24-hr urine samples collected within 24 hr; and d) evaluate the sensitivity and specificity of spot samples that were used to classify the individuals' 3-month average excretion measurements.
Urinary metal concentrations/excretions were expressed in the following three ways: a) as an uncorrected concentration (micrograms per liter); b) as a creatinine-corrected concentration, calculated by dividing the uncorrected concentration by the urinary creatinine concentration (micrograms per gram creatinine); and c) as the UER of each metal, computed by dividing the total mass of excretion by the amount of time since the previous void (micrograms per hour) (Akerstrom et al.
The apportionments of the within-person and between-person variances for metal measurements were similar based on the creatinine-corrected, creatinine as a covariate, and UER models.
The UERs in Table 1 can be contrasted with standard BMRs (extra risk) of 1%, 5%, and 10%, typically employed in the BMD method.
Using the profile likelihood method, the upper (one-sided) 95% confidence bound on the extra risk (UER) at a given dose, d, will, if used as the BMR in a standard BMD analysis, result in a BMDL that equals dose d (i.e., if the BMDL is defined as the lower one-sided 95% confidence bound on the BMD and is estimated under the profile likelihood method).
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