Topical Estradiol Gel Leading to Laboratory Error in Serum Estradiol Measurement: A Diagnostic Pitfall

Abstract

ABSTRACT

Estradiol gel is commonly used as an estrogen replacement therapy for patients with menopausal symptoms. Herein, we present a case of a patient with iatrogenic primary ovarian insufficiency who exhibited an abnormally elevated serum estradiol concentration (5634.0 pg/mL) during routine estradiol monitoring. A detailed interview revealed that the cause of these elevated levels was contamination of the needle used to draw her blood with gel from her skin. To the best of our knowledge, this is the first report of estradiol concentrations exceeding 2000 pg/mL due to such contamination. This phenomenon is not well known and is not described in package inserts or guidelines. There is a risk that misleadingly high serum estradiol concentrations may lead to inappropriate dose adjustments, potentially negatively affecting the health of the patients. Thus, clinicians must provide precise instructions to patients to avoid applying the gel around the area where venipuncture is to be performed.

---

Summary

• The contamination of blood samples with estradiol gel could cause misleadingly high serum estradiol concentrations, which may result in inappropriate dose adjustments, negatively affecting patients' health.
• Our report highlights the importance of informing patients about this issue.
• Including information on package inserts and guidelines may help prevent such a pitfall.

---

Introduction

Supplemental estrogen administration is a necessary component of management for treating patients who experience the loss of ovarian function before the age of 40 years, a condition known as primary ovarian insufficiency (POI). Owing to a decreased or complete lack of estrogen, patients often experience hormone-related health problems, such as hot flashes, anxiety, and vaginal dryness. Additionally, patients with POI may be at risk for long-term health complications, such as osteoporosis, heart or vascular disease, dyslipidemia, and dementia. The absorption of supplemental estrogen varies widely among individuals [1], and elevated serum estradiol (E2) concentrations may lead to side effects, including breast discomfort, increased vaginal discharge, venous thromboembolism, thrombophlebitis, and breast cancer, among others. Despite these potential risks, maintaining an adequate level of estrogen replacement is essential to achieve therapeutic benefits [2]. Therefore, there are certain guidelines, studies, and package inserts describing the necessity of measuring serum E2 concentrations routinely, or in cases with hyper-estrogenic symptoms or when there is no clinical response during estrogen replacement therapy (ERT) [1–4].

In this report, we present a case of a patient with iatrogenic POI who exhibited unexpectedly high serum E2 concentrations on a peripheral blood test during ERT, representing an example of a potential clinical pitfall in ERT management. Although underreported in the literature, elevated sex steroid levels due to topical contamination have recently been reported with both E2 and testosterone gels [5, 6], suggesting that this issue may be more common in clinical practice than currently recognized.

Case History

We present a case of a 38-year-old, gravida 1 para 0, Japanese woman who had undergone treatment for uterine cervical cancer (squamous cell carcinoma, International Federation of Gynecology and Obstetrics 2018 stage IIIC1r). Her height and body weight were 147.3 cm and 43.5 kg, respectively. She had no significant medical or family history.

The patient underwent concurrent chemoradiotherapy, which included a weekly cisplatin regimen (40 mg/m², 55 mg/week, total 275 mg), 55 Gy whole pelvic irradiation, and 18 Gy high-dose-rate intracavitary therapy using a remote after-loading system. Several months post-chemoradiotherapy, the patient became amenorrheic and began to experience hot flashes. She subsequently consulted her oncologist, who ordered a hormonal examination. Her blood test revealed undetectable serum E2 concentration (< 5.0 pg/mL, electrochemiluminescence immunoassay [ECLIA]) along with elevated serum follicle-stimulating hormone (FSH) concentration (97.50 mIU/mL, ECLIA). The patient was accordingly diagnosed with iatrogenic POI and was prescribed an estradiol patch (ESTRANA, Hisamitsu Pharmaceutical Co. Inc., 0.72 mg, every other day). However, shortly after using the E2 patch, she began experiencing side effects, including nausea and headache. She discontinued the patch after 10 days, and she continued to experience hot flashes during follow-up every 2 months. Twelve months after completing her cancer treatment, she was subsequently referred to our department.

Methods (Differential Diagnosis, Investigation, and Treatment)

We changed the dosage and form of her supplemental E2 administration to a half dose (1 push/0.9 g daily) of the estradiol 0.06% gel pump pack (L'ESTROGEL, Fuji Pharma Co. Ltd.), which was eventually increased to a full dose (2 pushes/1.8 g daily). Ultrasound revealed no endometrial thickening. Her symptoms subsided, and she successfully continued ERT with the E2 gel, with a scheduled blood test as per the manufacturer's instructions. At the 1-year follow-up, the serum E2 and FSH concentrations of the patient were 5634.0 pg/mL and 74.30 mIU/mL, respectively. As the serum E2 concentration was unexpectedly high, we re-evaluated both the serum E2 and FSH concentrations a few days later and obtained similarly elevated results (E2: 2850.0 pg/mL, FSH: 58.20 mIU/mL). Given that her serum E2 concentration dropped significantly to an undetectable level (E2: < 0.5 pg/mL, FSH: 91.00 mIU/mL) 1 month after cessation of use of the E2 gel, the elevated serum E2 concentration was evidently due to exogenous E2 administration (Figure 1).

[IMAGE OMITTED. SEE PDF]

Conclusion and Results (Outcome and Follow-Up)

We performed a detailed assessment to confirm how the patient was using the gel. During this process, she explained that she had “applied the gel from both shoulders to wrists in the morning,” after which she went to the hospital for her appointment and underwent blood sampling from the left cubital vein before noon. Based on this information, we suspected that the needle had become contaminated with the E2 gel during blood sampling. Therefore, we advised the patient to avoid applying the gel near both cubital fossae. One month later, her serum E2 concentration returned to expected levels (E2: 24.3 pg/mL, FSH: 75.20 mIU/mL), as depicted in Figure 1.

Discussion

We report a clinical pitfall that should be considered during estrogen supplementation. We observed an extremely elevated serum E2 concentration, which we attributed to contamination of a blood sample with the E2 gel, despite the appropriate dose being used. According to the package insert of the E2 gel, the average serum E2 concentration at steady state was 26.3 ± 4.8 pg/mL in the 1.25 g/day group and 60.8 ± 22.6 pg/mL in the 1.8 g/day group. However, the present case exhibited a 94-fold increase in the expected values.

Regarding the cause of this abnormally high serum E2 concentration, our concern was whether there had been an error in gel usage or an abnormality in E2 metabolism. The package insert specified that the gel should be applied to the broad area from the shoulders to the wrists once a day. Therefore, the patient correctly followed the manufacturer's instructions. As for E2 metabolism, no liver or renal dysfunction was observed in this patient. A potential drug interaction was also considered, as drugs that inhibit the drug-metabolizing enzyme cytochrome P450 (CYP3A4) can affect serum E2 concentrations [4, 7]. However, this cause was less likely as the patient was not taking any other medications and supplements. There was an extremely small possibility that the patient might have been experiencing endogenous E2 secretion. However, this was unlikely given that her ovarian function had been destroyed by the chemoradiotherapy. We also considered the possibility of an estrogen-producing tumor. However, this was ruled out because the serum E2 concentration sharply declined to below the sensitivity limit (0.5 pg/mL) once the patient stopped using the gel. In retrospect, we noted that the patient's serum FSH concentration remained high despite the elevated serum E2 concentration, suggesting that these high E2 levels did not accurately reflect her true serum E2 concentration.

Although determining that blood sample contamination was the cause of the patient's abnormally elevated serum E2 concentration initially posed a challenge, the solution was simple once we had identified the underlying cause. However, this clinical pitfall is poorly recognized. We searched PubMed using keywords such as “estradiol gel,” “serum concentration,” “contamination,” and “error” and found only two papers that discussed this issue in detail [1, 5]. The highest serum E2 concentration documented in these previous studies was less than 2000 pg/mL, even among the contaminated samples, which is significantly lower than the levels observed in the present case. Notably, this phenomenon is not addressed in the package inserts and guidelines [3, 4]. Therefore, we believe that it is likely that clinicians in other settings may have encountered this issue more frequently without recognizing it, particularly when serum E2 concentrations are in the range of 50–150 pg/mL. In such cases, misleadingly high serum E2 concentrations could potentially lead to inappropriate dose adjustments, negatively affecting the health of patients.

In conclusion, we report a case of a patient with iatrogenic POI who exhibited an unexpectedly elevated serum E2 concentration on a blood test during the course of gel ERT follow-up. Our report highlights the importance of clinicians informing patients about the potential for sample contamination before blood tests and ensuring careful screening of the area where the E2 gel is applied. Advising patients to apply gel to the thigh or areas away from phlebotomy sites before blood draws may be helpful. Furthermore, including this information on package inserts and guidelines may help prevent such a clinical pitfall.

Author Contributions

Takeki Sato: conceptualization, data curation, formal analysis, investigation, methodology, project administration, visualization, writing – original draft. Masahito Tachibana: data curation, supervision, writing – review and editing. Hiroaki Hiraga: data curation, writing – review and editing. Emi Yokoyama: data curation, writing – review and editing. Zen Watanabe: data curation, writing – review and editing. Masatoshi Saito: supervision, writing – review and editing.

Acknowledgments

The authors have nothing to report.

Ethics Statement

The Ethics Committee at Tohoku University Hospital approved this study (No. 36575).

Consent

Written informed consent was obtained from the patient for the publication of this case report.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.

References

T. Vihtamäki, T. Luukkaaka, and R. Tuimala, “Skin Contamination by Oestradiol Gel‐A Remarkable Source of Error in Plasma Oestradiol Measurements During Percutaneous Hormone Replacement Therapy,” Maturitas 48, no. 4 (2004): 347–353.

I. Sriprasert, N. Kono, R. Karim, et al., “Factors Associated With Serum Estradiol Levels Among Postmenopausal Women Using Hormone Therapy,” Obstetrics and Gynecology 136, no. 4 (2020): 675–684.

C. A. Stuenkel, S. R. Davis, A. Gompel, et al., “Treatment of Symptoms of the Menopause: An Endocrine Society Clinical Practice Guideline,” Journal of Clinical Endocrinology and Metabolism 100, no. 11 (2015): 3975–4011.

Japan Society of Obstetrics and Gynecology/Japan Association of Obstetricians and Gynecologists Editing/Supervision, Hormone Replacement Therapy Guideline 2017. [In Japanese] (Japan Society of Obstetrics and Gynecology Secretariat, 2017), 86–91.

R. A. Maggacis, A. S. Cheung, and B. J. Nolan, “Serum Estradiol Concentrations With Estradiol 0.06% Gel in Transgender and Gender‐Diverse Adults,” Clinical Endocrinology (2025).

A. P. Pichilingue, D. N. Greene, and M. D. Krasowski, “Falsely Elevated Serum Testosterone Measurements Resulting From Testosterone Topical Gel Contamination of the Venipuncture Site: Case Series and Retrospective Review,” Heliyon 9, no. 12 (2023): e22819.

H. Kuhl, “Pharmacology of Estrogens and Progestogens: Influence of Different Routes of Administration,” Climacteric 8, no. Suppl 1 (2005): 3–63.