What FSH (Follicle-Stimulating Hormone) levels suggest azoospermia versus oligospermia?

FSH Levels in Azoospermia vs. Oligospermia

FSH levels greater than 7.6 IU/L strongly suggest non-obstructive azoospermia, while FSH levels less than 7.6 IU/L typically indicate obstructive azoospermia or oligospermia. 1

Diagnostic Patterns

Azoospermia

• Non-obstructive azoospermia (NOA):

  • FSH levels typically elevated above 7.6 IU/L 1
  • Associated with testicular atrophy on physical examination 2
  • Normal semen volume and pH 2
  • Indicates primary testicular dysfunction or hypothalamic-pituitary-gonadal axis dysfunction 1

• Obstructive azoospermia:

  • FSH levels usually less than 7.6 IU/L 1
  • Normal testicular size and consistency 1
  • Often presents with low ejaculate volume (<1.4 mL) and acidic semen (pH <7.0) 1
  • May be associated with congenital bilateral absence of vas deferens or ejaculatory duct obstruction 1

Oligospermia

• Severe oligospermia (<5 million sperm/mL):

  • May have elevated FSH, but typically lower than in non-obstructive azoospermia 1, 3
  • FSH levels correlate inversely with sperm concentration 3
  • Requires genetic testing when accompanied by elevated FSH and testicular atrophy 1

• Moderate to mild oligospermia (5-15 million sperm/mL):

  • FSH levels may be normal or slightly elevated 4, 3
  • Less likely to have Y-chromosome microdeletions (only 0.8% in men with >1-5 million sperm/mL) 1

Clinical Implications

• FSH elevation correlates with the appearance of Sertoli cell only (SCO) tubules 5:

  • Mixed atrophy with unilateral focal SCO: FSH ~7.4 IU/L 5
  • Mixed atrophy with bilateral focal SCO: FSH ~10.7 IU/L 5
  • Bilateral or unilateral total SCO: FSH ~16.0 IU/L 5

• Normal FSH does not exclude severe spermatogenic dysfunction in all cases 5:

  • Some men with maturation arrest on histology can have normal FSH despite severe spermatogenic dysfunction 6
  • Therefore, FSH alone cannot definitively predict sperm retrieval success in all cases 6

Diagnostic Algorithm

1. Perform semen analysis with centrifugation to confirm azoospermia or determine degree of oligospermia 1, 6

2. Measure FSH levels:

   • If FSH >7.6 IU/L with testicular atrophy: Likely non-obstructive azoospermia 1
   • If FSH <7.6 IU/L with normal testicular size: Consider obstructive azoospermia or mild oligospermia 1
   • If FSH is borderline (around 7.6 IU/L): Additional testing needed 5

3. Additional testing based on FSH results:

   • For elevated FSH: Recommend karyotype testing and Y-chromosome microdeletion analysis 1
   • For normal FSH with azoospermia: Consider evaluation for obstruction 1

Important Caveats

• Confirmation of azoospermia requires centrifugation of the ejaculate and examination of the pellet under microscopy 1
• Complete AZFa and AZFb Y-chromosome microdeletions result in almost zero likelihood of sperm retrieval 1
• Hormonal levels (FSH, LH, inhibin B, AMH) have variable correlation with sperm retrieval outcomes in NOA 1
• FSH bioactivity may differ from immunoreactive FSH levels in some infertile men, though this is not routinely tested in clinical practice 4, 3