Skin contamination by oestradiol gel--a remarkable source of error in plasma oestradiol measurements during percutaneous hormone replacement therapy

Objectives: To study the consequence of skin contamination by oestradiol gel on circulating plasma oestradiol levels. Methods: We studied ten healthy, hysterectomized postmenopausal women who had used percutaneous oestradiol gel for at least 2 years. After wash-out period percutaneous dose of 1.5 mg 17β-oestradiol was administered once a day in the evening. The gel was applied with a bare or gloved hand to an arm or thigh according to the schedule. Blood samples for assay of plasma oestradiol concentrations were collected from both cubital veins 12 h after gel administration, at baseline and every time after using the gel, for 2 weeks. Results: Plasma oestradiol concentrations were significantly higher in the gel-contaminated samples: in the cubital vein of the gel-applying arm and in the cubital vein of the forearm on which the gel had been spread. Conclusions: Skin contamination by topical 17β-oestradiol can distort plasma oestradiol measurements by giving much higher oestradiol concentrations than in reality there are in the systemic circulation. This has an important meaning when tailoring individual oestrogen therapy.