How can a GnRH stimulation test be used to differentiate between adrenal and ovarian androgen-producing tumors?

GnRH Test for Differentiating Adrenal vs Ovarian Androgen-Producing Tumors

The GnRH stimulation test has limited utility for differentiating between adrenal and ovarian androgen-producing tumors, with very poor sensitivity (10%) despite high specificity, and should not be relied upon as a primary diagnostic tool for tumor localization 1.

Diagnostic Approach

Initial Biochemical Assessment

When evaluating suspected androgen-producing tumors, the first step is measuring baseline androgens:

• Testosterone >7 nmol/L suggests a tumor, though 25.9% of confirmed adrenal tumors fall below this threshold 2
• DHEAS >600 µg/dL (16,000 nmol/L) strongly indicates an adrenal source 3
• Combined testosterone and DHEAS assessment achieves 100% sensitivity for adrenal tumors 2

If DHEAS is normal but testosterone is markedly elevated (>2x upper limit), suspect ovarian source 3. Ovarian tumors typically show LH-dependent testosterone elevation that can be suppressed by GnRH agonists, estrogen-progestogen, or cyproterone acetate 3.

Role and Limitations of GnRH Testing

The GnRH analogue stimulation test operates on the principle that ovarian androgen production is gonadotropin-dependent, while adrenal production is not. However:

• Sensitivity is only 10% for identifying tumors, making it unreliable for ruling out ovarian sources 1
• Specificity is 100%, meaning a positive response (testosterone suppression >50%) confirms ovarian origin 1, 4
• The test may show paradoxical results, as some adrenal tumors demonstrate enhanced LH response to GnRH 5

Recommended Diagnostic Algorithm

1. Measure baseline testosterone and DHEAS

   • DHEAS >600 µg/dL → proceed directly to abdominal CT for adrenal imaging 3
   • Normal DHEAS with testosterone >2x normal → perform pelvic ultrasound for ovarian imaging 6

2. Imaging is superior to functional testing

   • CT for suspected adrenal tumors
   • Pelvic ultrasound for suspected ovarian tumors
   • Consider selective venous sampling if imaging is inconclusive (100% sensitivity) 1

3. GnRH testing may be considered only when:

   • Imaging is equivocal or negative
   • You need to confirm gonadotropin-dependence before surgery
   • Assessing therapeutic response potential in non-surgical candidates 7

Critical Pitfalls

• Do not rely on strict hormonal cutoffs alone: Up to 26% of confirmed adrenal tumors have testosterone <7 nmol/L or DHEAS <18.5 µmol/L 2
• Dexamethasone suppression testing can be misleading: ~30% of adrenal tumors show paradoxical androgen rise after dexamethasone 2
• Cortisol co-secretion occurs in 28% of adrenal tumors, requiring additional evaluation for Cushing's syndrome 2
• GnRH testing has poor negative predictive value: A negative test does not exclude ovarian pathology 1

Therapeutic Considerations

While GnRH analogues have poor diagnostic sensitivity, they demonstrate therapeutic utility:

• Can suppress testosterone by >50% in gonadotropin-dependent ovarian hyperandrogenism 4
• Provide a non-surgical option for patients with ovarian hyperthecosis or benign ovarian tumors who cannot undergo surgery 7, 8
• Dual diagnostic-therapeutic role in select cases of severe hyperandrogenism 7

The most reliable approach combines biochemical assessment (testosterone + DHEAS) with direct imaging (CT/ultrasound), reserving GnRH testing for specific scenarios where gonadotropin-dependence needs confirmation or as a therapeutic trial 6, 3.