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Letters
July 24/31, 2002

Measurement of Serum Estradiol Levels in Postmenopausal Women—Reply

Author Affiliations
 

Stephen J.LurieMD, PhD, Senior EditorIndividualAuthor

JAMA. 2002;288(4):450-451. doi:10.1001/jama.288.4.446

In Reply: We agree with Dr Stanczyk that it is preferable to measure very low levels of estradiol using assays that have a purification step and that have been tested for reproducibility at the very low levels of estradiol that we studied. According to SciCor (Covance) Central Laboratory Services (Indianapolis, Ind), the double antibody method that we used is specific to estradiol: there is 12.5% cross-reactivity with estrone and no more than 6% cross-reactivity with other estrogen metabolites, and no significant cross-reactivity with nonestrogens. Nevertheless, these measurements were made nearly 8 years ago for the purpose of determining whether participants were postmenopausal. We took advantage of those existing data to test our hypotheses. If the estradiol assay had less than optimal reliability, this would add random error to the estradiol levels. This random error would have caused us to underestimate the magnitude of the associations between estradiol, raloxifene treatment, and breast cancer risk, and thus our estimates are probably conservative. We are in the process of confirming these observations using different validated and standardized ultrasensitive assays of estradiol in other randomized trials of selective estrogen receptor modulators. Until these results are available, we reiterate that it is premature for clinicians to base decisions about use of selective estrogen receptor modulators on routinely available measurements of estradiol.

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