6 alpha-biotinylated estrone: novel tracer in competitive chemiluminescence immunoassay of estrone in serum.

We describe the development and validation of a labeled-hapten competitive immunoassay for determining total estrone in serum. For the hapten tracer we use the 6 alpha-biotinylated estrone derivative, 3-hydroxyestra-1,3,5(10)-trien-17-one 6 alpha-N-(epsilon-biotinyl)aminocaproamide (Bio-E1). A specific polyclonal rabbit anti-estrone antibody is indirectly bound via an immobilized donkey anti-rabbit antibody on microtiter plate wells. The amount of Bio-E1 bound is then measured with streptavidin-horseradish peroxidase conjugate, whereby the enzyme activity is quantified by an enhanced chemiluminometric method. For the assay, serum samples were extracted with solid-phase extraction cartridges. The assay dynamic range was 93-7400 pmol/L estrone, with a lower detection limit of 55 pmol/L. An interassay imprecision (CV) of 12-14%, a recovery rate between 80% and 110%, and a dilution linearity are demonstrated. Estrone serum concentrations were measured in healthy men and women and in women with polycystic ovary syndrome. Comparing the assay with a nonextraction RIA, we found an acceptable correlation for samples from 143 subjects of either sex. This enzyme immunoassay with biotin as the primary label and enhanced chemiluminescence signaling detection performs well for determining total estrone in serum and is readily adaptable to assays for other steroid hormones.