An Analysis of the Hydra Assay's Applicability and Reliability as a Developmental Toxicity Prescreen

A large and diverse group of chemicals was evaluated in the Hydra assay, and the outcomes were compared with those of standard developmental toxicity evaluations using data from pregnant mammals. Hydra correctly identified each of the substances previously found by in vivo tests to be uniquely hazardous to in utero development. Its overall accuracy was over 90%, and all of its errors were false positives. The fact that these positives were indeed false could have been established subsequently by routine testing in mammals. In no instance did the assay indicate that a chemical was not uniquely hazardous to the conceptus when higher level tests indicated that it was, i.e., 0 false negatives. The possible areas for continued refinement of the assay and expansion of its scope of use as well as perceived problems and limitations are discussed in detail.