Removing lead from bone: clinical implications of bone lead stores.
The chelating agent, CaNa2EDTA, has proven useful for both the diagnosis and treatment of lead poisoning. The EDTA lead-mobilization test has demonstrated the presence of excessive body lead stores when blood concentrations were "normal." The EDTA lead-mobilization test is, however, impractical because it requires injections and timed urine collections. Bone lead measured in biopsy specimens by atomic absorption spectroscopy shows a good correlation with chelatable lead. Over 95% of the body stores of lead are retained in bone with a biological half-life approximating two decades. The half-life of lead in blood, on the other hand, approximates one month. Bone, therefore, provides a good estimate of cumulative lead absorption. In vivo tibial K x-ray fluorescence (XRF) is a safe, specific and reliable technique for the non-invasive measurement of elevated bone lead concentrations. K XRF measures lead to a depth of about 2 cm in cortical bone and is largely independent of geometric factors because lead is measured relative to bone calcium. In vivo tibial K XRF can therefore replace the EDTA lead-mobilization test and bone biopsies for assessing body lead stores and for following the efficacy and endpoint of deleading during chelation therapy.