Within-person reproducibility of red blood cell mercury over a 10- to 15-year period among women in the Nurses’ Health Study II

Most epidemiologic studies of methylmercury (mehg) health effects rely on a single measurement of a mehg biomarker to assess long-term exposures. long-term reproducibility data are, therefore, needed to assess the reliability of a single measure to reflect long-term exposures. in this study, we assessed within-person reproducibility of red blood cell (rbc) mercury (hg), a marker of methyl-mercury, over 10–15 years in a sample of 57 women. fifty-seven women from the nurses’ health study ii provided two blood samples 10–15-years apart (median: 12 years), which were analyzed for mercury levels in the red blood cells (b-hg*). to characterize within-person reproducibility, we estimated correlation and intraclass correlation coefficients (r and icc) across the two samples. further, we compared different prediction models, including variables on fish and seafood consumption, for b-hg* at the first sample, using leave-one-out cross-validation to assess predictive ability. overall, we observed strong correlations over 10–15 years (r=0.69), as well as a high icc (0.67; 95% ci: 0.49, 0.79). fish and seafood consumption reported concurrently with the first b-hg* sample accounted for 26.8% of the variability in that b-hg*, giving a correlation of r=0.52. despite decreasing b-hg* levels over time, we observed strong correlations and high icc estimates across b-hg* measured 10–15 years apart, suggesting good relative within-person stability over time. our results indicate that a single measurement of b-hg* likely is adequate to represent long-term exposures.