Is low serum testosterone associated with impaired spermatogenesis and reduced male fertility?

The relationship between serum testosterone and male reproductive function is well-established in clinical practice, with testosterone serving as a fundamental biomarker for both sperm production and overall fertility potential. Major urological guidelines, including those from the AUA/ASRM and EAU, mandate testosterone screening for infertile men, noting that hypogonadism is a factor in approximately 10–15% of infertility cases.

Clinical evidence and fertility outcomes

• Sperm Parameters: Clinical studies consistently demonstrate that low serum testosterone (<300 ng/dL) is strongly associated with oligozoospermia (low sperm count) and azoospermia (absence of sperm).
• Success Rates: In the context of assisted reproduction, men with total testosterone levels below 264 ng/dL have shown significantly lower live birth rates following intrauterine insemination (IUI)—approximately 18.8%—compared to those with normal levels.
• Therapeutic Response: The effectiveness of treatments like clomiphene citrate or gonadotropin therapy, which improve sperm parameters by raising endogenous testosterone, reinforces the clinical link between testosterone levels and reproductive success.

Mechanistic explanations

• Intratesticular Testosterone (ITT): While serum levels are the standard clinical metric, the primary driver of spermatogenesis is ITT, which is typically 10 to 100 times more concentrated than serum testosterone.
• Sertoli Cell Function: Testosterone acts on Sertoli cells via androgen receptor (AR) signaling to maintain the blood-testis barrier and drive germ cell development through meiosis.
• HPG Axis Regulation: Low serum testosterone often reflects a broader disruption of the hypothalamic-pituitary-gonadal (HPG) axis. Reduced luteinizing hormone (LH) stimulation leads to both low systemic levels and insufficient ITT, causing spermatocyte arrest and seminiferous tubule atrophy.

Bottom line

Low serum testosterone is a reliable clinical indicator of impaired spermatogenesis and reduced fertility, though its impact is mediated through the critical requirement for high intratesticular testosterone concentrations to support viable sperm production.