What are the FSH (Follicle-Stimulating Hormone) thresholds for normospermia, oligospermia, and non-obstructive azoospermia?

FSH Thresholds for Normospermia, Oligospermia, and Non-Obstructive Azoospermia

FSH levels above 7.6 IU/L strongly suggest non-obstructive azoospermia, while levels between 4.5-7.6 IU/L are associated with oligospermia, and levels below 4.5 IU/L typically indicate normospermia. 1, 2

FSH Threshold Values and Semen Parameters

• FSH levels ≤4.5 IU/L are generally associated with normal sperm parameters (normospermia) 2
• FSH levels >4.5 IU/L show significantly increased risk of abnormal semen parameters, particularly affecting sperm concentration and morphology 2
• FSH levels >7.6 IU/L strongly correlate with non-obstructive azoospermia (NOA), with 89% of men with NOA having FSH above this threshold 1
• Men with FSH levels >7.5 IU/L have a five- to thirteen-fold higher risk of abnormal semen quality compared to men with FSH <2.8 IU/L 2

Correlation Between FSH and Testicular Histology

• Patients with obstructive azoospermia and normal testicular histology typically have normal FSH levels (mean 3.0 IU/L) 3
• Mixed atrophy without focal Sertoli cell only syndrome (SCO) correlates with mildly elevated FSH (mean 4.5 IU/L) 3
• Mixed atrophy with unilateral focal SCO shows moderate FSH elevation (mean 7.4 IU/L) 3
• Mixed atrophy with bilateral focal SCO presents with higher FSH levels (mean 10.7 IU/L) 3
• Bilateral or unilateral total Sertoli cell only syndrome shows the highest FSH levels (mean 16.0 IU/L) 3

Clinical Implications for Diagnosis

• FSH levels negatively correlate with the number of spermatogonia, meaning higher FSH generally indicates decreased sperm production 4
• Men with non-obstructive azoospermia typically present with low testicular volume, normal sperm volume, and elevated FSH values 5
• For azoospermic patients, FSH ≤7.6 IU/L with testicular long axis >4.6 cm suggests obstructive azoospermia in 96% of cases 1
• Conversely, FSH >7.6 IU/L or testicular long axis ≤4.6 cm indicates non-obstructive azoospermia in 89% of cases 1

Important Caveats and Limitations

• FSH levels alone cannot definitively predict sperm retrieval success in all cases of non-obstructive azoospermia 4, 6
• Men with maturation arrest on testicular histology can have normal FSH despite severe spermatogenic dysfunction 7, 6
• Positive sperm retrieval has been reported in up to 50% of NOA patients despite elevated FSH 5
• Some studies suggest that motile sperm can be found in non-obstructive azoospermic patients with FSH concentrations <30 mIU/mL 8
• The traditional "normal" range for FSH (often cited as 1.4-18.1 IU/L) may need reconsideration, as values >4.5 IU/L have been associated with abnormal semen parameters 2

Diagnostic Algorithm

• Confirm azoospermia with at least two semen analyses after centrifugation 5, 6
• Measure serum FSH, testosterone, and LH levels 4, 6
• Assess testicular size and consistency (normal-sized testes suggest obstructive azoospermia while atrophic testes indicate non-obstructive azoospermia) 4, 6
• Interpret FSH levels:
  • <4.5 IU/L: Likely normospermia or mild oligospermia 2
  • 4.5-7.6 IU/L: Moderate to severe oligospermia 2, 1

  • 7.6 IU/L: Likely non-obstructive azoospermia 1, 4

• Consider genetic testing (karyotype and Y-chromosome microdeletion analysis) for men with non-obstructive azoospermia 7, 4