I’ve been consulting for a while for a company that makes blood lead assays. It used to be that the lowest allowable level of lead was 10 ug/dL. Below this level, no action was needed whereas above this level, a repeat assay was proscribed to determine if the source of contamination was still present. The lead level that sparks chelation treatment is 45 ug/dL.
The cut-off of 10 makes one wonder. If a person (usually a child) has a level of 9.9 and another child has an undetectable lead level, do these two kids have the same risk for lead poisoning? (Note a lead assay measures lead exposure, not lead poisoning).
But now, the CDC has changed the allowable level to 5 ug/dL. This raises some strange possibilities. The parents of a child who previously had a lead level of 6 may not have been even notified of the result, but had the child just been tested they would be.
What has changed? One thing that has not changed is the biological role for lead in humans. There is none! And since higher levels of lead cause severe problems isn’t it likely that any level of lead is undesirable?