BONE LEAD MEASURED BY X-RAY-FLUORESCENCE - EPIDEMIOLOGIC METHODS

In vivo X-ray fluorescence (XRF) measurement of bone lead concentratio n (XRF) has emerged as an important technique for future epidemiologic al studies of long-term toxicity. Several issues germane to epidemiolo gic methodology need to be addressed, however. First, sources of varia bility in measurements of bone lead need to be quantified, including i mprecision related to the physical measurement itself and the variabil ity of lead deposition over the two main compartments of bones (cortic al vs. trabecular) and within each compartment Imprecision related to the physical measurement can be estimated for each individual measurem ent based on the variability of the signal and background. Second, app roaches to low-level data need to be debated. We argue for using the m inimal detection limit (MDL) to compare instruments and interpret indi vidual measurements; however, with regard to epidemiologic studies, we would abandon the MDL in favor of using all point estimates. in analy ses using bone lead as an independent variable, statistical techniques can be used to adjust regression estimates based on estimates of meas urement uncertainty and bone lead variability. Third, factors that can be expected to modify the relationship between bone lead and toxicity such as gravida history, endocrinological states, nutrition, and othe r important influences on bone metabolism, need to be identified and m easured in epidemiologic studies. By addressing these issues, investig ators will be able to maximize the utility of XRF measurements in envi ronmental epidemiologic studies.