FETAX INTERLABORATORY VALIDATION-STUDY - PHASE-III, PART 1 TESTING

The Frog Embryo Teratogenesis Assay-Xenopus (FETAX) is a 96-h whole em bryo developmental toxicity screening assay that can be used in ecotox icology and in detecting mammalian developmental toxicants when an in vitro metabolic activation system is employed, A standardized American Society for Testing and Materials (ASTM) guide for the conduct of FET AX has been published, along with a companion atlas that aids in embry o staging and identifying malformations, As part of the ASTM process, a three-phase interlaboratory validation study was undertaken to evalu ate the repeatability and reliability of FETAX, Seven different partic ipants collaborated in the study, In Phase I, FETAX proved to be more repeatable and reliable than many bioassays, However, some excessive v ariation was observed in a few laboratories, An initial lack of assay experience by some technicians caused variation, Phase II showed far l ess intra- and interlaboratory variability than Phase I, Non-teratogen s showed the most consistent results, while more variability was obser ved for the two teratogens tested, Interlaboratory coefficient of vari ation values for all endpoints ranged from 7.3 to 54.7, Phase III-Part 1, using coded samples and test concentration ranges selected by each laboratory, showed results similar to Phase I, Analysis of the causes of variation suggested that some technicians judged some embryos to b e malformed while others consistently judged similar embryos as normal , Concentration ranges tested by some of the laboratories varied great ly and a new protocol for selecting concentrations for initial testing was written to reduce variation from this source, Testing to date sug gests that FETAX is as repeatable and reliable as other standard bioas says.