Reproducibility of urinary beta 2-microglobulin and cadmium excretion among residents in a cadmium-polluted area during a 3-year period

Abstract

To assess the measurement error by using single exposure measurement in epidemiologic studies, reproducibility of urinary beta 2-microglobulin and cadmium excretion was evaluated among persons exposed to environmental cadmium. We measured urinary beta 2-microglobulin concentrations in 47 subjects four times and urinary cadmium concentrations in 48 subjects twice, during a 3-year period. Between-person and within-person variance components of these variables were estimated using a random-effects one-way analysis of variance model. The intraclass correlation coefficient (ICC) for urinary beta 2-microglobulin concentration, when expressed as microg/g creatinine and microg/l, was 0.92 and 0.89, respectively. The ICC for standardized urinary cadmium concentration (expressed as microg/g creatinine) was 0.81, while it decreased to 0.33 without standardization. The findings suggest that single measurement of urinary beta 2-microglobulin and cadmium, when expressed as a function of creatinine, can reliably estimate average levels over at least a 3-year period. Standardization of concentration using urinary creatinine improved reproducibility especially for urinary cadmium excretion.