Assessing estrogen exposure from transdermal estradiol patch therapy using a dried urine collection and a GC-MS/MS assay

Background: Transdermal estradiol patch therapy is often dosed based on patient reported symptoms. Although dosing based on serum estradiol concentrations has been considered, serum sampling is too invasive and inconvenient to use in real-world settings. The primary aim of this study was to determine if a dried urine assay could be used to assess estrogen exposure resulting from transdermal estradiol patch therapy at increasing doses.

Methods: This was a retrospective analysis of clinical laboratory data. Urinary estrogen profiles of postmenopausal women being treated with transdermal estradiol patches at differing doses (age = 56.8 ± 7.5) were selected from the database along with the profiles of women on no therapy for comparison (age = 55.1 ± 9.5). Metabolite concentrations were obtained using a multi-spot dried urine collection and a gas chromatography-tandem mass spectrometry assay. The Jonckheere-Terpstra test was used to assess for ordered differences across dose groups to determine if dose-dependent increases in urinary estrogens occurred with increasing doses.

Results: Median concentrations of estradiol and other estrogen metabolites increased with increasing doses of transdermal estradiol patch therapy (p < 0.001; Jonckheere-Terpstra test). For women who collected samples before and after initiating therapy, there were significant differences between before and after concentrations of estradiol and other estrogen metabolites.

Conclusion: This large study conducted using real-world data demonstrated that a dried urine assay offers a viable method of assessing estrogen exposure differences that occur with the use of differing doses of transdermal estradiol patches. Further studies with prospective designs that include outcome measures are needed to confirm the findings of this study.