Arsenic exposure: Reliability of spot urine samples in epidemiological studies

Urinary arsenic concentrations are often used as biomarkers of arsenic exposure. The 24-hour urine sample has been considered the most reliable sample type. First morning void (FMV) samples are more concentrated. However, 24-hour samples and FMV samples are more expensive and difficult to collect compared with spot samples. FMV samples and their corresponding spot urine samples from 131 participants enrolled in a case-control study in southeastern Michigan have been used to determine the correlation between FMV and spot urine samples. Urine samples were analyzed using HPLC and ICPMS for seven different arsenic species: AsB, As[III], DMA[V], DMA[III], MMA[V], MMA[III], and As[V]. Correlation procedures and Kappa scores were calculated to evaluate the relationship between FMV and spot urine samples after adjusting for specific gravity. There were no significant differences between urinary arsenic concentrations for the different samples types. A significant correlation (0.65 p<0.001) was observed for total arsenic concentration (As[III] + DMA[V]+ MMA[V] +As[V]) between FMV samples and their corresponding spot samples. Spot and FMV samples were highly correlated for MMA[V] (0.730 p<0.0001), while DMA[V] remained strongly correlated (0.614 p<0.0001). The results of this study suggest that spot samples are adequate for measuring arsenic exposure using urinary arsenic species concentrations. In addition to measuring arsenic exposure, MMA[V] showed a strong correlation between FMV and spot urine samples. MMA[V] excretion has been related to an increase risk of arsenic-related diseases. The collection of spot urine samples, instead of 24-hour or FMV urine samples, may reduce budget and logistic strategies in epidemiological studies.