Can estrogen levels peak if a transgender patient takes their oestradiol (estrogen) prior to getting their blood drawn for estrogen measurement?

From the Guidelines

Yes, estrogen levels can peak if a transgender patient takes their oestradiol (estrogen) medication shortly before getting their blood drawn for estrogen measurement. This is known as a "peak" level rather than a "trough" level. For accurate monitoring of hormone therapy, it's generally recommended that transgender patients have their blood drawn for estrogen measurement just before their next scheduled dose, which provides a trough level.

Key Considerations

• If using oral estradiol, blood should ideally be drawn 24 hours after the last dose for once-daily dosing, or 12 hours after for twice-daily dosing, as suggested by the dosing regimens outlined in 1.
• For injectable estradiol valerate or cypionate, blood tests are best done midway between injections or just before the next injection.
• Transdermal patches or gels, such as those described in 1, produce more stable levels but should still be measured consistently in relation to application times. The timing matters because estradiol levels can vary significantly throughout the day based on when medication was last taken, especially with oral and injectable forms which create more pronounced peaks and troughs in blood levels, as noted in the context of hormonal replacement therapy 1.

Administration Routes and Timing

• The transdermal administration of 17β-estradiol seems to be the preferred route as it mimics the physiological serum estradiol concentrations providing a better safety profile than oral formulations 1.
• Estrogen doses should be increased not earlier than 6-monthly over a period of 24 months, as suggested by analyses comparing the mean estradiol levels achieved during induction and circulating estradiol concentrations in healthy girls 1.

From the FDA Drug Label

These systems increased estradiol levels above baseline within 4 hours and maintained respective mean levels of 25 and 79 pg/mL above baseline following application to the abdomen; slightly higher mean levels of 88 pg/mL above baseline were observed following application to the buttocks The corresponding pharmacokinetic parameters are summarized in Table 2 †Peak plasma concentration. The half-life values calculated after dosing with the estradiol transdermal system (twice-weekly) ranged from 5.9 to 7. 7 hours.

Estrogen Levels: Estrogen levels can peak if a transgender patient takes their oestradiol prior to getting their blood drawn for estrogen measurement.

• Time to Peak: The drug label states that estradiol levels increase above baseline within 4 hours of application.
• Peak Concentration: The peak plasma concentration (Cmax) of estradiol is reached, with values ranging from 46 to 145 pg/mL, depending on the dosage.
• Half-life: The half-life of estradiol is between 5.9 and 7.7 hours, which means that the concentration of estradiol in the blood will decrease by half within this time frame. 2

From the Research

Estrogen Levels and Timing of Oestradiol Intake

• Estrogen levels can fluctuate based on the timing of oestradiol intake, as the body absorbs and processes the hormone at different rates 3, 4.
• The study on hormonal treatment of transgender women with oral estradiol found a positive correlation between estradiol dose and 17-β estradiol levels, indicating that estrogen levels can peak after oestradiol intake 3.
• However, the study also noted that there was wide individual variability in the amount of estradiol required to achieve desired serum levels, suggesting that the timing of oestradiol intake may not be the only factor affecting estrogen levels 3.

Factors Affecting Estrogen Levels

• The biological effects of hormone replacement therapy, including estrogen levels, can vary depending on the serum estradiol levels achieved 5.
• The study on biological effects of hormone replacement therapy found that different tissues have different sensitivities to estradiol, and that the effects of estradiol on various clinical endpoints, such as bone mineral density and lipid metabolism, can vary depending on the serum estradiol levels 5.
• Other factors, such as age, dose, and method of administration, can also affect estrogen levels, as seen in the study on the range and variation in serum estradiol concentration in perimenopausal and postmenopausal women treated with transdermal estradiol 6.

Clinical Implications

• The timing of oestradiol intake can impact estrogen levels, and healthcare providers should consider this when monitoring hormone levels in transgender patients 7, 4.
• Individualized treatment plans, taking into account factors such as dose, method of administration, and serum estradiol levels, can help ensure that transgender patients achieve optimal estrogen levels and minimize potential risks and complications 3, 7, 4.