Evaluation of a sensitive immunoenzymometric assay for thyrotropin suitable for emergency and paediatric use

This short communication compares a luminescent-labelled immunometric assay (BeriLux) with an enzyme-labelled immunometric assay (NovaPath) for thyrotropin determinations. The NovaPath assay lends itself to paediatric use, because it only uses 25 microliters sample, and to emergency use, because the main incubation can be reduced to 30 minutes. The correlation between both kits was acceptable (r = 0.825, n = 167 data pairs) although the NovaPath kit gave lower values than the BeriLux it (Median-BeriLux 1.00 mU/l, NovaPath 0.70 mU/l, p less than 0.001 = Wilcoxon Test). From 167 sera (range less than 0.01-44 mU/l) 3 gave discrepant values, being euthyroid in the BeriLux kit and hyperthyroid in the NovaPath kit. All 3 patients were undergoing thiamazole (Favistan) therapy at the time of sampling. The coefficients of variation were lower in the BeriLux kit (intraassay less than 4.5%, interassay less than 5.5% for the range 0.1-50 mU/l) than in the NovaPath kit (intraassay less than 7.5%, interassay less than 12.5%). This reflects the larger dynamic range (signal/noise ratio) of the BeriLux kit.