Sign In

News Article

Home \ News \ News Article

Accuracy of Estradiol Measurements: New Challenges

Accurate measurement of estradiol, particularly at low concentrations, is important in several clinical situations including evaluating hormone status in post-menopausal women and in women undergoing treatment for breast cancer.  LifeLabs uses automated immunoassays for the determination of estradiol in patient samples. All immunoassays are susceptible to interference from heterophilic antibodies.   They are also susceptible to interference from metabolites of the parent molecule and from structurally related molecules which may cross-react with the assay antibodies.  Antibody specificity to the target molecule in immunoassays and cross reactivity with structurally related molecules may vary from one immunoassay to another.  This leads to variability in assay results for the same specimen when tested by different method and some assays may give more accurate (true) results than others depending on the specific sample and potential interferents. Results should always be interpreted in light of the complete clinical picture and treatment plan.


Two specific sources of interference in immunoassays for estradiol have been highlighted by current information, including published literature. A brief outline follows for your consideration.



Fulvestrant (Faslodex®) is a selective estrogen receptor (ER) antagonist indicated for use in clinical situations including in metastatic breast cancer.  It is a structural analog of 17β-estradiol which binds to the receptor.  The parent drug and/or its metabolites may therefore interfere with the accuracy of immunoassays for estradiol by interacting with the antibodies used in the estradiol method.


Published data indicates that specimens from patients on Fulvestrant may generate significant falsely elevated assay results when analyzed by direct immunoassays1, 2. False elevations may be as high as ten-fold and appear to depend on the concentration of Fulvesrant and/or metabolites of both the drug (Fulvestrant) and the assay target (estradiol).


Aromatase Inhibitors

The primary non-ovarian source of estradiol is adipose tissue where the enzyme aromatase converts testosterone and androstenedione to estradiol and estrone respectively.  Knowledge of this metabolic pathway has led to the widespread use of aromatase inhibitors (AIs) as one treatment for breast cancer.  AIs may be used sequentially with the drug Tamoxifen3.


Two issues related to the measurement of estradiol in patients on AI treatment are of concern.  The first is the accuracy and reliability of the commonly used immunoassays at the low estradiol concentrations expected in these patients.  Evidence suggests that immunoassays produce substantially higher values than mass spectrometry-based assays4-7. While mass-spectrometry assays have improved specificity, these methods are technically challenging and not currently in routine diagnostic use in Canada.


The second issue is that some AIs (Formestane and Exemestane) are structurally highly related to estradiol.  Therefore, it is anticipated that these medications and/or their metabolites may interfere in direct immunoassays for estradiol4,7 .  While there is continuing discussion, there is no direct evidence that supports this possible interference.  It is worth noting that the steroidal AIs bind irreversibly to aromatase and so may not be available to act as interferents in immunoassays for estradiol.



  1. Misperception of estrogen activity in patients treated with an estrogen receptor antagonist.  Elguero et al; Am J Obstetrics & Gynecology, 2014; e1


  1. Field Safety Notice, Siemens Healthcare Diagnostics, CC 16-03.A.OUS –CA; Jan 2016


  1. Breast Cancer Chemoprevention: Old and New Approaches.  Cazzaniga, M. & Bonanni, B. J Biomed Biotechnol. 2012: 985260. Published online 2012 Jul 17. doi:10.1155/2012/985260


  1. Deficiencies in immunoassay methods used to monitor serum Estradiol levels during aromatase inhibitor treatment in postmenopausal breast cancer patients. Jaque et al. SpringerPlus 2013, 2:5


  1. Analysis of Estrogens in Serum and Plasma from Postmenopausal Women: Past Present, and Future.  Ian A. Blair.  Steroids. 2010 Apr; 75(4-5): 297–306.

Published online 2010 Jan 28. doi:  10.1016/j.steroids.2010.01.012


  1. Superiority of gas chromatography/tandem mass spectrometry assay (GC/MS/MS) for estradiol for monitoring of aromatase inhibitor therapy.  Santen et al. Steroids, 72(8); 2007; p666-71


  1. Interpreting Plasma Estrogen Levels in Breast Cancer: Caution Needed.  E. J. Folkerd et al. J Clin Oncology 2014

Did you know that you can book your appointment online?

Book an Appointment