Thyroid stimulating hormone measurement using a third generation immunometric assay.

After an initial evaluation of the standard procedure for performance of a third generation TSH (thyroid stimulating hormone) assay (Amerlite TSH-30) modifications were made to standardize the timing of measurement of light emission following signal reagent addition. By adopting this optimized procedure, a significant improvement in assay sensitivity was achieved when compared to a second generation TSH assay (DAKO). Using the optimized assay the sensitivity was 0.003 mU/L (20 replicates of zero) or 0.009 mU/L [22% CV (coefficient of variation) from the precision profile]. Recovery of added TSH and parallelism of the assay were good. A significant negative bias was detected for the Amerlite TSH-30 assay when compared to the DAKO assay (log y = 0.92 log x-0.33, n = 210). Excellent discrimination was achieved between euthyroid, hypothyroid and thyrotoxic subjects. A high percentage of thyrotoxic patients had undetectable TSH and the spread of values between thyrotoxic and euthyroid was greater with the third generation assay. In patients receiving thyroxine therapy a higher percentage had detectable TSH values. The optimized Amerlite TSH 30 assay offers improved assay performance when compared to a second generation assay.