What is the cut-off testicular volume for low sperm production?

Testicular Volume Cut-off for Low Sperm Production

Testicular volumes less than 12 mL are definitively considered atrophic and associated with impaired spermatogenesis, while volumes of 15 mL represent the lower threshold of normal testicular function for adequate sperm production. 1

Critical Volume Thresholds

The 12 mL Threshold (Definitive Atrophy)

• Volumes below 12 mL are associated with impaired spermatogenesis, higher risk of intratubular germ cell neoplasia, and potential infertility. 1
• Men with testicular volumes less than 12 mL typically present with elevated FSH levels (>7.6 IU/L), indicating primary testicular dysfunction and non-obstructive azoospermia. 2
• Patients with volumes less than 10 mL are typically azoospermic, while volumes less than 20 mL are associated with severe oligozoospermia. 3
• A testicular volume threshold of 12 mL has good predictive ability for detecting non-obstructive azoospermia (NOA) status. 4

The 15 mL Threshold (Lower Limit of Normal)

• A testicular volume of 15 mL is generally considered the lower limit of normal, with volumes of 15-18 mL associated with normal spermatogenesis and adequate fertility potential. 1
• Testicular volume thresholds of 15 mL have good predictive ability for detecting oligoasthenoteratozoospermia (OAT) status in infertile men. 4
• The median testicular volume in fertile men is 22.5 mL, compared to 15.0 mL in infertile men. 4

The 30 mL Threshold (Optimal Function)

• The critical testicular volume indicating normal testicular function is approximately 30 mL, with sperm density falling below normal limits in patients with volumes less than 30 mL. 3
• Testicular volume has the strongest positive correlation with sperm density, followed by total sperm count per ejaculate, total motile sperm count, and percentage of motile sperm. 3

Correlation with Sperm Parameters

Direct Relationships

• Mean testicular size strongly correlates with total sperm count and sperm concentration. 1
• Testicular volume positively correlates with total testosterone, sperm concentration, and progressive sperm motility in infertile men. 4
• Right testicular volume (RTV) is the best independent factor associated with testicular function, determined by sperm concentration (β=.292), sperm motility rate (β=.227), and total testosterone (β=.245). 5
• All biofunctional sperm parameters (mitochondrial membrane potential, phosphatidylserine externalization, chromatin compactness, and DNA fragmentation) are strongly negatively correlated with testicular volume. 6

FSH Correlation

• Testicular volume has the strongest negative correlation with serum FSH concentrations, followed by serum LH concentrations. 3
• FSH levels >7.6 IU/L typically suggest non-obstructive azoospermia (spermatogenic failure), while normal FSH levels suggest obstructive azoospermia. 2
• Multiple regression analysis reveals that serum FSH concentration is the only significant factor determining testicular volume. 3

Clinical Assessment Approach

Measurement Technique

• The Prader orchidometer is a good surrogate for testicular volume measurement and is easier to perform and more cost-effective than ultrasound in clinical practice. 1
• Use the Lambert formula for ultrasound calculation: Length × Width × Height × 0.71. 1
• High-frequency probes (>10 MHz) should be used to maximize resolution and accurate caliper placement. 1

When to Investigate Further

• Testicular volumes less than 12 mL warrant further investigation, especially when associated with infertility concerns or history of cryptorchidism. 1
• Size discrepancy between testes greater than 2 mL or 20% warrants ultrasound evaluation to exclude pathology, regardless of absolute volume. 1
• RTV less than 15 mL is the only positive predictor for low testicular function (odds ratio=2.79). 5

Important Clinical Caveats

• FSH levels alone cannot definitively predict sperm retrieval success—up to 50% of men with non-obstructive azoospermia and elevated FSH still have retrievable sperm with testicular sperm extraction. 2
• Men with maturation arrest on testicular histology can have normal FSH and testicular volume despite severe spermatogenic dysfunction. 2
• Even "normal-sized" testes in the context of infertility should prompt semen analysis, as testicular volume alone cannot definitively predict fertility status. 1
• Conditions associated with smaller testicular volumes include history of cryptorchidism, varicocele presence, and genetic abnormalities (Klinefelter syndrome, Y-chromosome microdeletions). 1, 2