How to track your estradiol over time

Estradiol is the test people on hormone therapy watch most closely. On feminizing therapy, it is the number a dose gets adjusted against. In fertility treatment, it may be checked several times in one cycle. In menopause, results turn up even though dosing is usually guided by symptoms. On testosterone therapy, it is checked when breast symptoms suggest some of the testosterone is becoming estradiol.

It is also one of the hardest results to compare from one draw to the next. The number depends on how long ago you took your dose, how you take it, the method the lab used, and, if you have a cycle, what day of it you were on. A history of results is only useful when you know those things about each one.

What the test measures

Estradiol (E2) is the main estrogen made by the ovaries before menopause. Smaller amounts are made in other tissues, including from testosterone, which the enzyme aromatase converts to estradiol. A blood test measures the estradiol in your serum at the moment of the draw.

That last part matters. Estradiol is not a long average like A1c. It moves across a menstrual cycle, and on treatment it rises and falls with every dose. Each result is a snapshot of one point on a curve.

People who track estradiol closely include:

• Transgender women and nonbinary people on feminizing therapy, where estradiol and testosterone are both checked to guide the dose.
• People on menopausal hormone therapy, who may get results even though dosing is usually guided by symptoms.
• People in fertility treatment, where estradiol is part of cycle monitoring.
• Men and others on testosterone therapy, where estradiol is sometimes checked because some testosterone becomes estradiol.

The numbers on the report

In the United States, estradiol is usually reported in pg/mL. Much of the rest of the world uses pmol/L. Using estradiol’s molar mass of 272.38 g/mol, the conversion is:

pmol/L = pg/mL × 3.671 (or pg/mL = pmol/L ÷ 3.671)

A value of 200 means something very different in each unit, so keep the unit with every result. The lab unit converter handles this and other common conversions.

Reference ranges

The range printed next to an estradiol result is often several ranges: one for each phase of the menstrual cycle, one after menopause, and one for men. For anyone with a cycle, the phase is the result: the same person can be low on one day and several times higher a week later. Your cycle shows up in your labs covers what moves when, and why a cycle day belongs with every result if you have one.

If you are on hormone therapy, none of the printed ranges are your target. The lab does not know why the test was ordered. A “high” flag on a result drawn the day after an injection may be exactly what was expected. Why are lab reference ranges different? explains where printed ranges come from.

Targets on feminizing therapy

The Endocrine Society’s 2017 guideline for gender-dysphoric and gender-incongruent people says serum estradiol should not exceed the peak physiologic range of 100 to 200 pg/mL, with testosterone below 50 ng/dL. These are the levels of premenopausal women, used as a stand-in. The WPATH Standards of Care, version 8, reprint the same numbers in their monitoring table, worded as estradiol “should be in the range of 100-200 pg/mL.”

Not every guideline uses those numbers. Sherbourne Health’s quick reference guide, used widely in Canada, says most patients attain considerable feminization at estradiol levels between 200 and 500 pmol/L. That is about 54 to 136 pg/mL, lower than the U.S. range and in different units. If your care moves between clinics or countries, the target may change even when your dose does not.

Testosterone is the other half of the picture on feminizing therapy. How to track your testosterone over time covers units, assays, and charting for it.

Menopausal hormone therapy

For menopause, The Menopause Society’s 2022 hormone therapy position statement says salivary and urine hormone testing to determine dosing are unreliable and not recommended, and that serum hormone testing is rarely needed. It gives the reasons: differences in how hormones are absorbed, changes through the day, and variation between and within people. Dosing is usually guided by symptoms.

People still end up with estradiol results, from a checkup, a fertility question, or a clinician who wanted one. They are worth keeping, but read them with the dose and timing next to them, not against a target.

Testosterone therapy

The AUA testosterone deficiency guideline recommends measuring estradiol in men with breast enlargement before treatment, in those who develop breast symptoms on treatment, and in anyone taking an aromatase inhibitor. Its follow-up testing table lists estradiol at baseline and alongside total testosterone as optional for everyone else.

The assay matters more than usual

Most estradiol tests are immunoassays: an antibody binds the hormone and the machine measures the signal. They work well at the levels seen in a menstrual cycle or a fertility cycle. They work poorly at low levels.

An Endocrine Society position statement on estradiol measurement found that most direct immunoassays cannot reliably measure below about 30 to 100 pg/mL. That is too high for children, postmenopausal women, men, and women on aromatase inhibitors. In one study it cites, a radioimmunoassay read men’s estradiol at an average of 33 pg/mL where mass spectrometry read 21. Related compounds can also cross-react with the antibody. The statement describes interference that pushed measured values as high as ten times the true value.

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) separates estradiol from look-alike molecules before measuring it, which makes it more specific at low levels. Labs often put the method in the test name: “Estradiol, Ultrasensitive, LC/MS/MS” or “Estradiol, Sensitive”. The CDC’s Hormone Standardization Program (HoSt) certifies the accuracy of estradiol tests, as it does for testosterone.

For tracking, the lesson is simple. A history that switches between an immunoassay and LC-MS/MS can show a step that is only the change of method, especially at low levels. Note the method with each result.

A few specific things can throw an immunoassay off:

• Biotin. Many immunoassays use a biotin-streptavidin system, and high-dose biotin supplements can interfere. The University of Iowa’s laboratory lists estradiol among affected tests and notes the error can go up or down depending on the assay. A review of biotin interference cites advice to stop biotin at least 48 hours before a blood draw. Ask your clinician before stopping anything.
• Fulvestrant. This breast cancer drug is shaped like estradiol and can cross-react with estradiol immunoassays, giving falsely high results. Singapore’s Health Sciences Authority advises considering LC-MS instead and noting fulvestrant on the test request.
• Estrogens that are not estradiol. The Endocrine Society’s 2017 guideline notes that blood tests cannot monitor conjugated estrogens or synthetic estrogens. If you take one of those, an estradiol result does not measure your dose.

Why the time since your last dose matters

On treatment, the time between your last dose and the draw can matter more than the dose itself. The Endocrine Society says serum estradiol can be used to monitor oral, transdermal, and intramuscular estradiol, but that injectable and sublingual estradiol produce more rapid peaks with greater swings, which makes them harder to monitor.

Injections. In a 1980 study of single 5 mg injections, estradiol peaked about 2 days after estradiol valerate and about 4 days after estradiol cypionate. Levels stayed raised for 7 to 8 days after valerate and about 11 days after cypionate. Those were single doses in a small group, not repeated doses, but the shape is the point: a draw on day 2 and a draw on day 6 of the same schedule describe different moments.

Patches and sublingual tablets. A 2024 randomized trial in transgender women drew blood before the morning sublingual dose, or on the morning a patch was due for replacement, so every level was a trough. The authors chose troughs to make the arms comparable.

Oral tablets, gels, and pellets. The guidelines above do not set a draw time for these. Ask your clinician what timing they want, and then keep it the same.

Timing also explains some surprising results. A 2025 chart review of 35 people on guideline-concordant feminizing doses at one center found that 91% of first follow-up levels on injections were above 200 pg/mL when drawn midway between weekly injections, and that most patch levels were below 100. It was a small study. It shows how far the route alone can move the number.

The practical rule is the one the testosterone guidelines use: pick a time relative to your dose, such as the trough or the midpoint between injections, and draw there every time. Record the date and time of the last dose with every result.

How often it is tested

• Feminizing therapy: the Endocrine Society and WPATH SOC8 both recommend measuring hormone levels every 3 months in the first year, then once or twice a year.
• Menopausal therapy: rarely, according to The Menopause Society.
• Testosterone therapy: when there are breast symptoms or an aromatase inhibitor, per the AUA, and optionally otherwise.
• Fertility treatment: during ovarian stimulation, clinics follow the response with ultrasound, often with estradiol blood tests too. A Cochrane review found no clear difference in pregnancy rates between ultrasound alone and ultrasound plus estradiol. Those results belong to one treatment cycle and are read by the clinic in that context. Keep them, but keep them grouped by cycle.
• Cycle evaluation: on specific cycle days, covered in the cycle post.

What counts as a real change

Before comparing two estradiol results, check that they are comparable at all:

• Same route and dose? A change from pills to patches, or a new dose, makes the later result a new baseline.
• Same timing? A trough and a peak are not a trend. On injections, compare results drawn on the same day of the schedule.
• Same method and lab? An immunoassay result next to an LC-MS/MS result can differ for reasons unrelated to you, especially below about 30 to 100 pg/mL.
• Same cycle phase? If you have a cycle, compare like phases.
• Did testosterone move with it? On feminizing therapy, the pair tells more than either alone.

If all of that holds and the number still moved, it is more likely to be real. When one result is far from your others for no obvious reason, a repeat drawn the usual way is the fair test. Did the medication actually do anything? covers reading before-and-after results fairly.

Things that move estradiol

• Dose, route, and product. A switch from oral to transdermal, or from valerate to cypionate, changes the whole curve.
• Timing of the draw, the menstrual cycle, and the assay, as above.
• Biotin and fulvestrant, for immunoassays.
• Missed or late doses. A draw after a missed patch change or a late injection reads like a lower dose.

None of these make the result wrong. They make it a result that needs a note.

What to record with each result

For each estradiol result, keep:

Estradiol shows up under a few names: Estradiol, Estradiol (E2), Estradiol, Sensitive, and Estradiol, Ultrasensitive, LC/MS/MS. Some of those names tell you the method. Merge the ones measured the same way, and think before merging an immunoassay series with an LC-MS/MS one, since the step between them may be the method.

Charting it

A few choices make an estradiol chart honest:

• Space points by date. Four draws in the first year and one a year after that should not look evenly spaced.
• Mark every dose and route change. The chart is a series of plateaus, one per regimen, more than a single line.
• Chart testosterone alongside it on feminizing therapy, so you see both targets at once.
• Use your own target as the shaded range, not the lab’s cycle-phase ranges.
• Mark results drawn at a different time from the rest, or set them aside when you read the trend.
• Keep one unit. Convert pmol/L to pg/mL, or the reverse, before charting.

How to track your lab results over time has the general method for any test.

Tracking estradiol in HealthViewer

HealthViewer is a lab results tracker that runs on your own computer. It imports estradiol from lab report PDFs, MyChart downloads, and direct connections to your health system. Results from a direct connection that carry the standard code for serum estradiol are filed as “Estradiol”. Results in pmol/L are converted so they share one chart with results in pg/mL, and the chart title shows the unit in use.

Names from PDFs that include the method, such as “Estradiol, Sensitive” or “Estradiol by TMS”, stay as their own tests. In the Test Catalog, use Merge… to combine the ones measured the same way. In the same place, set a custom reference range such as your target, and Trends shades it with a Custom range label instead of the lab’s range.

The built-in Reproductive Hormones tag gathers estradiol, progesterone, LH, FSH, and prolactin. Testosterone is not in it, so add the tag to testosterone yourself if you want both in one filter. The overlay view puts estradiol and testosterone on one chart.

Enter each dose, route, or product as its own period in Medications, and medication markers show where each one started and stopped. When you open a result, it lists the medications you had recorded as active on that date. Each result also has a notes field, a good place for “trough, patch due today” or “day 3 after injection”. A journal note on the date of a lab or method change shows up on the chart when you turn on journal markers.

If you log periods in Cycle, each result drawn while you were tracking shows its cycle day and estimated phase, with a short note on how estradiol changes across the cycle.

Everything stays in an encrypted file on your computer, with no account and no cloud service. Getting Started walks through the first import.

This post is general information, not medical advice. Talk to your clinician about your estradiol results and before starting, stopping, or changing any treatment.