L-line x-ray fluorescence of cortical bone lead compared with the CaNa₂EDTA test in lead-toxic children: Public health implications

Mild to moderate lead toxicity (blood lead, 25-55 μg/dl) is a preventable pediatric illness affecting several million preschool children ('lead-toxic children') in the United States. In-hospital lead-chelation treatment is predicated upon a positive CaNa₂EDTA test, which is difficult to perform and impractical in large populations. After the development of an L-line x-ray fluorescence technique (LXRF) that measures cortical bone lead content safely, rapidly, and non-invasively, this study was initiated in lead-toxic children to compare LXRF with the CaNa₂EDTA test. Moreover, LXRF provided the opportunity to quantify bone lead content. From blood lead and LXRF alone, 90% of lead-toxic children were correctly classified as being CaNa₂EDTA-positive or -negative. In 76% of 59 lead-toxic children, bone lead values measured by LXRF were equal to or greater than those measured in normal and industrially exposed adults. These results indicate that LXRF may be capable of replacing the CaNa₂EDTA test. When considered with the known neurotoxic effects on children of 'low levels' of exposure to lead, these results also suggest that either an excessively narrow margin of safety or insufficient safety is provided by present U.S. guidelines, which classify an elevated blood lead concentration as 25 μg/dl or greater.