Analytic variability and clinical significance of different assays for serum estradiol

Recent reports in the clinical laboratory literature have raised questions about the accuracy of different methods of measuring serum estradiol. To determine whether between-method variability was clinically significant, we used five different commercial radioimmunoassay methods to measure the concentration of estradiol in sera from nine patients undergoing induction of ovulation for gamete intrafallopian transfer. There were large differences between the estradiol concentrations measured in the same samples by the different methods. Furthermore, apparent changes in concentration that would be regarded as clinically significant may reflect nothing more than the imprecision of the assay. Physicians using serum estradiol measurements to support therapeutic decisions should be aware that an excessive reliance on those measurements may be misleading.