The Use of Hematological Effects in the Development of Minimal Risk Levels

The Agency for Toxic Substances and Disease Registry (ATSDR) derives minimal risk levels (MRLs) to assist in evaluating risk of adverse health effects in individuals exposed to hazardous substances. MRLs are derived from published values identifying no-observed-adverse-effect levels (NOAELs) or lowest-observed-adverse-effect levels (LOAELs) in animal or human studies. The most sensitive end points are used. To date, 4 inhalation MRLs and 13 oral MRLs have been derived from hematological end points for 12 substances. This paper provides a brief overview of the hematological system, examples of hematological end points, and the MRL for substances with hematological end points.