How do I perform a GnRH stimulation test to differentiate ovarian from adrenal sources of excess androgen in an adult with unexplained hyperandrogenism?

GnRH Stimulation Test Protocol for Differentiating Ovarian from Adrenal Hyperandrogenism

The GnRH stimulation test should be performed with prior adrenal suppression using dexamethasone, followed by administration of a GnRH agonist (such as nafarelin or triptorelin) with serial measurement of 17-hydroxyprogesterone (17-OHP) as the primary endpoint to confirm ovarian androgen excess. 1

Test Protocol

Step 1: Adrenal Suppression Phase

• Administer dexamethasone 0.5 mg orally at lunch, dinner, and bedtime on Day 1
• Continue 0.5 mg at breakfast, lunch, dinner, and bedtime on Day 2
• Give final 0.5 mg dose at breakfast on Day 3 1

Purpose: This suppresses adrenal androgen production, allowing isolated assessment of ovarian contribution.

Step 2: Baseline Sampling

• Within 2 hours after the final dexamethasone dose, obtain three blood samples at 20-minute intervals
• Pool equal aliquots to create the baseline sample
• Measure: testosterone, DHEAS, 17-OHP, cortisol, LH, FSH 1

Step 3: GnRH Agonist Administration

• Administer GnRH agonist (nafarelin or triptorelin 100 mcg subcutaneously) 1, 2
• Collect blood samples at intervals over 24-25 hours
• Measure: 17-OHP, testosterone, androstenedione, estradiol, gonadotropins 1, 3

Interpretation

Ovarian hyperandrogenism is confirmed by:

• Supranormal 17-OHP response to GnRH agonist stimulation (the key diagnostic endpoint) 1, 3
• Elevated testosterone response while DHEAS remains suppressed 1
• This pattern indicates functional ovarian hyperandrogenism (FOH), present in approximately 58% of hyperandrogenic women 3

Adrenal hyperandrogenism is indicated by:

• Testosterone suppression >40% AND DHEAS suppression >60% with dexamethasone alone 1
• Lack of 17-OHP hyperresponse to GnRH agonist 1

Combined ovarian-adrenal hyperandrogenism:

• Testosterone suppression <40% with dexamethasone 1
• Elevated 17-OHP response to GnRH agonist 1

Critical Caveats

This test is primarily a research tool, not routine clinical practice 1. The AACE guidelines explicitly state this test "is useful only in clinical research of PCOS to identify the presence of 17-hydroxylase dysfunction" 1.

For clinical practice, simpler approaches are preferred:

• The 2-day dexamethasone suppression test alone adequately differentiates adrenal from ovarian sources in most cases 1
• Baseline hormone measurements (testosterone, free testosterone, DHEAS, 17-OHP) combined with clinical assessment are usually sufficient 4, 5

Important limitations:

• In postmenopausal women, the GnRH analogue test has only 10% sensitivity (95% CI: 1.1%-46.7%) for detecting virilizing tumors, making it unreliable in this population 6
• The test requires specialized laboratory capabilities for accurate low-level androgen measurement 1
• Peak 17-OHP after GnRH agonist correlates with free testosterone levels (r=0.75, p<0.001), but doesn't always correlate with ultrasound findings of polycystic ovaries (only 54% concordance) 3

When to Consider This Test

Reserve GnRH stimulation testing for:

• Research protocols investigating PCOS pathophysiology 1
• Refractory cases where standard evaluation is inconclusive 7
• Consideration of GnRH agonist therapy for severe ovarian hyperandrogenism 7

For routine clinical differentiation, use the standard 2-day dexamethasone suppression test instead 1, which provides adequate information to guide therapy without the complexity and cost of GnRH agonist stimulation.