What FSH (Follicle-Stimulating Hormone) levels are associated with azoospermia?

FSH Levels and Azoospermia

FSH levels above 14.6 mIU/mL are strongly associated with azoospermia, particularly in cases of non-obstructive azoospermia due to primary testicular dysfunction. 1

Relationship Between FSH and Spermatogenesis

FSH is a key hormone in male fertility evaluation, with normal levels typically ranging between 1.5-8 mIU/mL 2. The relationship between FSH and spermatogenesis follows these patterns:

• Elevated FSH levels (>14.6 mIU/mL) are negatively correlated with the number of spermatogonia and strongly suggest primary testicular dysfunction 2, 1
• Normal FSH levels with azoospermia may indicate obstructive causes rather than spermatogenic failure 3
• Very low FSH levels (<1.0 mIU/mL) may indicate hypogonadotropic hypogonadism, which can also cause azoospermia but through a different mechanism 4

FSH Levels and Testicular Histology

FSH levels correlate with specific testicular histological patterns:

• Highest FSH levels (mean 16.0 mIU/mL): Found in Sertoli cell only syndrome (SCOS), where there is a complete absence of germ cells 3
• Moderately elevated FSH (10.7 mIU/mL): Associated with mixed atrophy with bilateral focal Sertoli cell only pattern 3
• Mildly elevated FSH (7.4 mIU/mL): Seen in mixed atrophy with unilateral focal Sertoli cell only pattern 3
• Normal FSH (3.0-4.5 mIU/mL): Typically found in obstructive azoospermia with normal histology or in hypospermatogenesis 3

Clinical Implications for Sperm Retrieval

The FSH level has important implications for predicting sperm retrieval success:

• FSH levels above 14.6 mIU/mL predict poor outcomes for microsurgical testicular sperm extraction (micro-TESE) with a sensitivity of 83.5% and specificity of 80.3% 1
• Men with non-obstructive azoospermia (NOA) typically have low testicular volume, normal sperm volume, and high FSH values 5
• The presence of hypospermatogenesis on testicular biopsy is associated with better sperm retrieval outcomes compared to maturation arrest or SCOS 5

Diagnostic Algorithm

1. Measure serum FSH level:

   • If FSH > 14.6 mIU/mL: High probability of non-obstructive azoospermia with poor sperm retrieval outcomes
   • If FSH is normal (1.5-8 mIU/mL): Consider obstructive causes or focal spermatogenesis
   • If FSH is very low (<1.0 mIU/mL): Consider hypogonadotropic hypogonadism

2. Correlate with other hormones:

   • Check LH, testosterone, inhibin B, and AMH levels to complete the hormonal profile
   • These hormones provide additional information about testicular function 5, 2

3. Consider testicular volume:

   • Low testicular volume with high FSH strongly suggests non-obstructive azoospermia
   • Normal testicular volume with normal FSH suggests obstructive azoospermia

Treatment Considerations

For men with azoospermia and abnormal FSH levels:

• High FSH: Micro-TESE may be considered, but success rates are lower (approximately 33.6% without hormonal optimization) 6
• Optimizing hormonal levels: Medical treatment with clomiphene citrate, hCG, and hMG to achieve target FSH levels (1.5 times initial level) and testosterone (600-800 ng/dL) may improve sperm retrieval rates to approximately 57% 6
• Very low FSH: Replacement therapy with hMG or recombinant FSH may restore spermatogenesis in cases of isolated FSH deficiency 4

Important Caveats

• FSH alone cannot definitively diagnose the cause of azoospermia; it should be interpreted in conjunction with clinical findings and other hormonal parameters
• Normal FSH does not exclude severe spermatogenic impairment in individual cases 3
• Genetic factors such as Y-chromosome microdeletions significantly impact sperm retrieval outcomes regardless of FSH levels; complete AZFa and AZFb microdeletions make sperm retrieval virtually impossible 5
• FSH levels may fluctuate, so multiple measurements may be necessary for accurate assessment