Evaluation of nonisotopic alternatives for hormone determination in toxicology studies

Assessment of the endocrine function in toxicology studies implies hormone determination in a number of animal species. Radioimmunoassay, (RIA) consti tutes the most widely used methodology for this purpose. RIA, however, pres ents important disadvantages inherent in the use of radiosotopes. In an att empt to look for nonisotopic alternatives to animal hormone dosage, two com mercial, nonisotopic assays for the direct measurement of total human thyro xine concentration were compared with an RIA used routinely in our laborato ry. Total thyroxine (T-4) in the miniature pig was the parameter chosen for this comparison study Several protocols, using identical miniature-pig sam ples, were used to compare stability, precision, sensitivity accuracy, and bias. Precision and sensitivity studies determined the useful detection ran ge for RIA, enzyme immunoassay (EIA), and luminescent immunoassay (LIA), wh ich were 0.95-9.50 mu g/dL, 2.70-13.00 mu g/dL, and 0.45-20 mu g/dL, respec tively. Matrix-effect studies showed that only LIA was influenced by EDTA p lasma, and that the other methods were not sensitive to the different matri x tested. Lot-to-lot differences in the EIA method were significantly great er than those with the other methods. The radioimmunoassay and the automate d Luminescent technique gave the best results in this Evaluation study. The general application of the LIA method in veterinary endocrinology remains dependent on the further development of commercial detection kits.