Indicators of internal dose of lead in relation to derangement in heme synthesis.

Simultaneous measurements of Pb-B, Pb-U, chelatable lead, ALA-U and EP have been made in a group a asymptomatic children with increased lead absorption. Although the group is small, the results are internally consistent and show linear dose-effect relationships between Pb-U and chelatable lead (indicators of dose) and ALA-U and EP (indicators of lead's effect on heme synthesis). The data show, however, that Pb-B in a rather narrow range (48-68 mug Pb) is not a reliable indicator of the internal dose of lead. These results, as well as others, raise questions concerning the validity of relying exclusively on Pb-B in the clinical management of groups such as young children in old houses and lead-exposed workmen who are at increased risk for plumbism; The results suggest that chelatable lead is most closely related to lead's inhibitory effect on heme synthesis and that, biologically, it may serve as the best "chemical biopsy" of soft tissue lead concentration; A simple AAS method for measureing chelatable lead in urine is described; A new wet digestion technique which is compatible with ASV is also described. EP is apparently a better predictor of chelatable lead than Pb-B. Micro tests for EP, especially the zinc protoporphyrin fraction, are simple and highly useful in monitoring long-term trends in soft tissue levels in individual patients.