How to prepare for the ‘Estradiol’ test: rules for taking it

Estradiol is the main human estrogen, and a test for it is needed by both women and men. However, the rules for taking it differ: in women everything is decided by the phase of the menstrual cycle, in men — by the accuracy of the method, because the hormone concentrations are low. The editorial team explains how to prepare for the test in order to get a result you can rely on.

Why estradiol is measured

Estradiol (E2) in women is produced mainly by the ovarian follicles; in men it is formed chiefly from testosterone under the action of the enzyme aromatase in adipose, muscle and bone tissue and in the brain. In both sexes the hormone is important for bone health, lipid metabolism, vascular function, libido and cognitive function.

In women, the test is ordered to assess ovarian function, in cycle disorders, infertility, during ovulation stimulation and in perimenopause. In men — in gynecomastia, symptoms of hypogonadism, during testosterone replacement therapy and when estrogen-producing tumours are suspected.

The importance of estrogens for the male body was well demonstrated by the study of Finkelstein and colleagues (2013) in the New England Journal of Medicine. When aromatization was blocked in men, sexual function and indicators related to adipose tissue deteriorated, even though testosterone levels were sufficient. That is, ‘zero’ estradiol in men is not a goal but a problem.

Because of this, correct measurement of estradiol has practical significance: an inaccurate result may become a reason for unjustified treatment or, conversely, mask a real disorder.

For women: choosing the day of the cycle

The concentration of estradiol in women changes severalfold over the menstrual cycle. In the early follicular phase it is low, before ovulation it reaches a peak, then decreases and forms a second, smaller rise in the luteal phase. So the same figure may be normal on one day and a deviation on another.

For a baseline assessment of ovarian function, estradiol is usually taken on day 2–5 of the cycle — together with FSH and LH. In this window an elevated estradiol helps interpret FSH correctly: high estrogen can ‘mask’ an FSH rise through feedback.

For monitoring follicle growth in reproductive medicine, estradiol is measured on days prescribed by the doctor, often several times in a row. For assessing the luteal phase — usually together with progesterone about a week before the expected menstruation.

With an irregular cycle, in perimenopause or against a background of hormonal contraception, the standard ‘days’ lose their meaning. In such cases the timing of the draw is determined by the doctor, and the referral should indicate the date of the last menstruation and the drugs you are taking.

While taking combined oral contraceptives, the body's own secretion of estradiol is suppressed, and the ethinylestradiol in the tablets is not measured correctly by standard estradiol tests. Therefore the result during this period does not reflect ovarian function.

For men: why the method matters

In men, children and postmenopausal women, estradiol concentrations are low. It is precisely in this range that ordinary immunoassays work worst. The Endocrine Society position statement on estradiol measurement (Rosner et al., 2013) concluded that many immunoassays have insufficient accuracy and specificity for low concentrations.

The reason is the cross-reactivity of antibodies with other steroids and their metabolites, as well as matrix effects. The result may be either overestimated or underestimated, and the difference between laboratories can be substantial.

Liquid chromatography with tandem mass spectrometry (LC-MS/MS) has better specificity and sensitivity. The review by Stanczyk and Clarke (2010) describes the advantages of mass spectrometry for steroid hormones, while noting that it too requires careful validation.

For men on testosterone replacement therapy, the estradiol level depends on the testosterone level and the time after drug administration, so the timing of the draw is determined by the doctor. The Endocrine Society guideline (Bhasin et al., 2018) recommends assessing estradiol in men primarily when gynecomastia or relevant symptoms are present, rather than routinely.

General preparation rules and medications

For estradiol there is no such pronounced food effect as for testosterone, but in practice it is often taken as part of a hormone panel. Therefore unified conditions are recommended: morning, fasting or after a light breakfast if the laboratory allows — but if the same draw includes testosterone, then strictly fasting.

• for women — coordinate the day of the cycle with the doctor and indicate the date of the last menstruation;
• have it done in the morning, at a stable time, preferably fasting;
• avoid intense training, alcohol and stress the day before;
• report all hormonal drugs, contraceptives, aromatase inhibitors, SERMs;
• report biotin intake.

Biotin in high doses can distort estradiol immunoassays that use the streptavidin–biotin system. In 2017 the FDA published a separate warning about this. How long you need to avoid biotin before the test — check with the laboratory.

The list of drugs that affect estradiol is broad: estrogens and progestins, hormonal contraception, testosterone and other androgens, aromatase inhibitors, selective estrogen receptor modulators, gonadotropins. You must not discontinue prescribed therapy on your own — the doctor needs information, not a ‘clean’ result at the cost of a break in treatment.

A significant change in body weight also affects estradiol, because adipose tissue is a site of aromatization. A result obtained during a period of sharp weight gain or loss should be interpreted with an adjustment for this.

Common interpretation mistakes

The first mistake is to compare a woman's result with a ‘general’ norm without taking the day of the cycle into account. Laboratory forms usually give separate intervals for the follicular, ovulatory and luteal phases, as well as for postmenopause.

The second is to draw conclusions about an ‘estrogen excess’ in a man from a single insensitive immunoassay. A mistaken interpretation may lead to unjustified suppression of estradiol, which, as studies have shown, has a negative effect on bones, libido and lipids.

The third is confusion with units: pg/mL and pmol/L. To convert pg/mL to pmol/L, multiply by approximately 3,67. Without taking units into account, figures from different sources cannot be compared.

The fourth is ignoring context. Estradiol is assessed together with FSH, LH, testosterone, SHBG and prolactin, and in women — with ultrasound data. A single indicator rarely answers a clinical question.

Editorial conclusions

The estradiol test is technically simple but requires the correct choice of timing and method. For women the key is the day of the cycle; for men and postmenopausal women — the sensitivity and specificity of the laboratory test.

Basic preparation: morning draw, stable conditions, informing the doctor about hormonal agents and biotin. For monitoring over time it is worth using one laboratory.

Any decisions on adjusting estrogens are made by a doctor taking into account symptoms and a set of tests.

The editorial team advises also reading our articles on preparing for the FSH, progesterone and SHBG tests.

References

1. Rosner W, Hankinson SE, Sluss PM, Vesper HW, Wierman ME. Challenges to the measurement of estradiol: an Endocrine Society position statement. J Clin Endocrinol Metab. 2013;98(4):1376–1387.
2. Finkelstein JS, Lee H, Burnett-Bowie SA, et al. Gonadal steroids and body composition, strength, and sexual function in men. N Engl J Med. 2013;369(11):1011–1022.
3. Stanczyk FZ, Clarke NJ. Advantages and challenges of mass spectrometry assays for steroid hormones. J Steroid Biochem Mol Biol. 2010;121(3–5):491–495.
4. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744.
5. Strauss JF, Barbieri RL (eds). Yen & Jaffe's Reproductive Endocrinology. 8th ed. Elsevier; 2019.
6. U.S. Food and Drug Administration. The FDA warns that biotin may interfere with lab tests: FDA safety communication. 2017.