Ultrasensitive Semiautomated Chemiluminescent Immunoassay for Estradiol

The availability of rapid, non-extraction-based estradiol-17β immunoassays has been important in clinical settings where prompt turnaround time is required, including in vitro fertilization programs, and in large-scale research programs where large numbers of samples are processed. However, the inaccuracy of estradiol-17β assay results has been recognized for some time, as indicated in the Textbook of Reproductive Medicine by L.R. Boots (1), in which he states: “Everyone measures estradiol levels and it is probably assumed that few if any problems exist with this assay…. The most common use of estradiol levels is in relation to levels of estradiol during ovulation stimulation and every assay provides clinically relevant results. These results are clearly inaccurate but usually precise” (1). In the First and Second E2 International Workshops (2), problems associated with the analysis of estradiol-17β were fully discussed. The First E2 International Workshop focused on the need for more specific, precise, and sensitive estradiol-17β assays, and the Second E2 International Workshop explored various means of increasing accuracy in the measurement of estradiol-17β. By consensus, the use of a panel of 22 samples confirmed by isotope dilution–gas chromatography–mass spectrometry (ID-GC-MS) (2) was made available for use in assay development. Indications of a lack of accuracy are also provided by examining survey programs, such as those offered by the College of American Pathologists, that reveal large differences in estradiol-17β values obtained on the same sample. Modern serum assays for estradiol-17β claim detection limits as low as 40 pmol/L or lower, but they lack sufficient sensitivity for pediatric or postmenopausal specimens and are frequently unable to provide adequate analytical precision and accuracy in samples from human males. In postmenopausal women, circulating estradiol-17β is usually 147 pmol/L are rare. In …