Estradiol-17beta measurement in women receiving conjugated estrogens. Dissociation between two commercial methods

To investigate problems associated with measurement of estradiol-17beta (E2) in hormone replacement therapy (HRT), two commercial immunometric methods (Coat-A-Count E2 and Immulyze E2) were used to assay E2 concentrations and the two results were expressed as E2 ratios. Samples were obtained from 97 Japanese women receiving HRT and 168 unmedicated women. The largest differences between methods (P < 0.001) occurred in patients receiving oral conjugated estrogen (CE), while the best concordance was found in unmedicated women; like these controls, patients receiving oral estriol or transdermal E2 showed no significant difference between methods. Defining an E2 ratio > or = 2.0 as an abnormal discordance, the mean E2 ratio and the frequency of abnormal discordance in the CE group were 2.15 +/- 1.18 and 43.6%, respectively. No abnormal discordance for E2 occurred in other groups. In serial serum samples from the control group, no significant difference was seen between the mean E2 ratio at first measurement and those at a subsequent measurement. Similarly, no significant difference in the ratio was seen when two serial samples from CE patients were compared. However, E2 ratios after prescription of CE were significantly higher than before treatment in all patients. In conclusion, although measurement of E2 is important in patients receiving HRT, validity of the test methods must be carefully weighed for patients receiving CE.