Estradiol immunoassay cross-reactivity and similarity predictions. A. The plot shows the estradiol reference ranges for males, non-pregnant females, and pregnant females (highlighted in yellow) in comparison to the predicted apparent estradiol concentrations produced on the Roche Elecsys Estradiol II assay by estrone (females), ethinyl estradiol, and estriol (non-pregnant and pregnant females). Table 3 contains the concentration ranges and percent cross-reactivity values from which the estimated apparent estradiol concentrations are derived. B. Two-dimensional similarity of compounds to estradiol is shown, sorted by degree of cross-reactivity in the Roche Estradiol II assay (horizontal line in each column indicates average similarity within that group). Similarity values vary from 0 to 1, with 1 being maximally similar. The compounds are subdivided into categories of strong cross-reactivity (5% or greater, black circles), weak cross-reactivity (0.5-4.9%, red squares), very weak cross-reactivity (0.05-0.49%, blue triangles), and no cross-reactivity (<0.05%, green diamonds) to the Roche Estradiol II assay (complete list of compounds and associated cross-reactivities and 2D similarities is in Additional file 1).