Reliability of spot urine samples in assessing arsenic exposure

Urinary arsenic concentration is often used as a biomarker of arsenic exposure. First morning void (FMV) and spot urine samples from 131 participants in southeastern Michigan were analyzed using an HPLC-IC-PMS system for six different arsenic species: arsenobetaine (AsB), arsenite (As[III]), arsenate (As[V]), methylarsonous acid MMA[III], methylarsenic acid MMA[V], and dimethylarsenic DMA[V]. Bland-Altman plots, intraclass correlation coefficients (ICCs), and Pearson correlation procedures were used to evaluate the relationship between the arsenic species in FMV and spot urine collections after normalizing the samples by specific gravity. DMA[III] and MMA[III] were not detected in any of the samples. The sum of As[III], As[V], MMA[V], and DMA[V] was designated SumAs. The ICC between SumAs in FMV and SumAs in spot samples was 0.90. The ICC showed that 90% of variation comes from between individuals and not within individuals. A significant correlation (r=0.80 p<0.001) was observed between FMV and spot samples for SumAs. The spot sample were a good predictor of the MMA[V] (r=0.83 p<0.0001), and DMA[V] (r=0.77 p<0.0001) in the FMV sample. These associations suggest that either FMV or spot samples can be used as an adequate bioindicator of arsenic metabolites in human urine. The benefit of using spot urine samples, instead of 24-h or FMV urine samples, is the potential reduction in budgetary and logistic requirements in epidemiological studies.