Are hormone levels reliable for diagnosing Polycystic Ovary Syndrome (PCOS) in a patient with an Implanon (etonogestrel) implant in place?

Hormone Testing for PCOS with Implanon In Place

Hormone levels for diagnosing PCOS are NOT reliable while Implanon (etonogestrel implant) is in place, and the implant should be removed or allowed to expire before testing. The progestin-only implant suppresses the hypothalamic-pituitary-ovarian axis, fundamentally altering the hormonal milieu required for accurate PCOS diagnosis.

Why Hormonal Testing is Unreliable with Implanon

Etonogestrel disrupts the key hormonal patterns needed for PCOS diagnosis:

• LH/FSH ratio becomes unreliable: The progestin suppresses gonadotropin secretion, eliminating the characteristic elevated LH or elevated LH/FSH ratio seen in many PCOS patients 1
• Ovulation is suppressed: PCOS diagnosis requires demonstrating oligo-anovulation as a baseline state, but Implanon itself causes anovulation through its mechanism of action 2
• Androgen interpretation is compromised: While total testosterone remains the best single biochemical marker for PCOS (74% sensitivity, 86% specificity), the progestin-induced changes in SHBG and the suppressed ovarian function alter the hormonal context 1, 2

Diagnostic Approach in This Patient

The Rotterdam criteria require 2 of 3 features: oligo/anovulation, hyperandrogenism (clinical or biochemical), and polycystic ovarian morphology 2. Here's how to proceed:

What CAN Be Done Now (Without Removing Implanon)

• Ultrasound assessment remains valid: The presence of Implanon does not interfere with ovarian imaging since the device sits within the endometrial cavity while ovaries are separate lateral pelvic structures 3
• Transvaginal ultrasound with ≥8 MHz frequency should document follicle number per ovary (FNPO) ≥20 follicles (2-9mm) or ovarian volume >10 mL 3, 2
• Clinical hyperandrogenism assessment: Document hirsutism, acne, or androgenic alopecia, which reflect long-term androgen exposure and are not acutely affected by the implant 2
• Historical menstrual patterns: Review her menstrual cycle characteristics BEFORE Implanon placement—cycle length >35 days suggests chronic anovulation 2

What CANNOT Be Done Reliably Now

• Biochemical hyperandrogenism testing: Total testosterone via LC-MS/MS (the gold standard with 74% sensitivity, 86% specificity) and calculated free testosterone (89% sensitivity, 83% specificity) require testing in the absence of hormonal contraception 1, 2
• LH, FSH, and LH/FSH ratio: These are suppressed by the progestin and cannot be interpreted 4
• AMH levels: While AMH is elevated in PCOS and less affected by hormonal contraception than gonadotropins, it is not yet recommended for clinical diagnosis due to lack of standardization and established cut-offs 1

Recommended Clinical Algorithm

Step 1: Assess what can be determined NOW

• Perform transvaginal ultrasound to evaluate for PCOM (FNPO ≥20 or ovarian volume >10 mL) 3, 2
• Document clinical signs of hyperandrogenism 2
• Obtain detailed menstrual history from BEFORE Implanon placement 2

Step 2: If ultrasound shows PCOM AND she had oligomenorrhea before Implanon

• PCOS diagnosis can be made based on these two Rotterdam criteria without hormonal testing 2
• Proceed with metabolic screening: fasting glucose, lipid panel, screen for type 2 diabetes 2

Step 3: If diagnosis remains uncertain

• Remove Implanon or wait for expiration (effective for 3 years)
• Wait at least 2-3 menstrual cycles after removal to allow the hypothalamic-pituitary-ovarian axis to recover
• Then obtain: total testosterone via LC-MS/MS, SHBG, calculated free testosterone using Vermeulen equation, and consider androstenedione 1, 2

Critical Pitfalls to Avoid

• Do not rely on LH/FSH ratio: Even without contraception, this has only 41-44% sensitivity for PCOS and should be abandoned as a diagnostic criterion 4
• Do not use direct immunoassay for free testosterone: It is highly inaccurate; always calculate free testosterone from high-quality total testosterone and SHBG measurements 1
• Do not diagnose based on ultrasound alone: Up to one-third of reproductive-aged women without PCOS have polycystic ovarian morphology 2
• Ensure she is >8 years post-menarche: Ultrasound should not be used for PCOS diagnosis in younger women due to high false-positive rates from normal multifollicular ovaries 1, 2

In summary, remove the Implanon first if biochemical confirmation is needed, or make the diagnosis based on historical oligomenorrhea plus current ultrasound findings if both are clearly abnormal.