Estradiol Serum Levels are Crucial to Understand Physiological/Clinical Setting in Both Sexes: Limits of Measurement of Low Estradiol and Evaluation of a Sensitive Immunoassay

Background: Measure of serum 17β-Estradiol is essential to understand physiology, development and health of reproductive processes in both sexes. Commercially immunoassays are not enough sensitive and accurate to assess low concentrations of E2. Purpose of this study was to compare a new sensitive immunoassay for estradiol measurement with respect to method current in our laboratory and to evaluate the performance of the new method. Methods: Four pools of patient sera with E2 concentrations close to clinical decision values were prepared. To test the repeatability of new method the 5x5 protocol was used and CVs were calculated. To evaluate the performance of new method, 50 samples with E2 concentrations covering the whole measurable interval were selected and assayed. Linearity dilution, LoB (Limit of Blank) and LoD (Limit of Detection) were determined. Results: The new assay showed good total repeatability demonstrated by low CV values, and good linear relationship with respect to current method (R=0.9926) as demonstrated by linear regression. Non-parametric regression showed for the new method a slight constant and proportional systematic error that, however, resulted not significant from difference plot analysis, with a general tendency to overestimate results for the current method. Performances of the new method resulted acceptable within the maximum admissible error derived from the literature, and a good linearity over a wide range of dilutions was showed. LoD value confirmed an amelioration in measurement of low estradiol. Conclusion: In conclusion, sensitive assay is suitable to replace the method used in our laboratory with significant improvement in the measurement of low serum estradiol levels.