Lead Poisoning: An Update

摘要

Lead (Pb) poisoning can be assessed at 3 levels: the fundamental biochemical effects, subclinical organ dysfunction, and clinical disease. The presence of Pb in a child's blood sample is an indicator that exposure and absorption have occurred. The blood Pb level (BLL) is a measure of potential toxicity because it is correlated with various health outcomes in groups of children. However, there are limitations to interpreting individual results. What is measured is not plasma Pb, the immediate and most threatening component of blood Pb, which can leave the blood compartment and enter cells. Rather, due to historical laboratory limitations, it is overwhelmingly (～98%) red blood cell Pb content that is assessed. Thus, the BLL is a surrogate measure 2 steps removed from tissue cell Pb, the site of most toxicity. In addition, the reside time (similar to half-life, a term that is strictly defined as the time for radioactivity of an isotope to fall by 50%) of Pb atoms in blood is very different from that in the organs where it accumulates. If Pb atoms are injected into blood, half are gone in approximately 3 weeks. In contrast, those that reach and enter brain cells remain for 1 to 2 years. Most Pb in the body accumulated through long-term exposure is found in the skeleton, where it can remain for years to decades.