Low Free Testosterone and Sexual Function
The claim is partially true: low free testosterone can indeed affect libido and orgasm strength even when total testosterone is normal or high, but the assertion about semen expulsion versus production is not well-supported by clinical evidence. 1
The Free Testosterone Phenomenon
Men with obesity and hypogonadism commonly have low total testosterone due to decreased sex hormone-binding globulin (SHBG), but may maintain normal free testosterone levels. However, a subset will have frankly low free testosterone despite normal or even elevated total testosterone, typically due to increased aromatization of testosterone to estradiol in adipose tissue, which suppresses pituitary luteinizing hormone secretion. 1
When evaluating any man with sexual symptoms, measuring morning serum free testosterone by equilibrium dialysis is essential, as total testosterone alone can be misleading. 1
Impact on Sexual Function
Libido and Desire
Low free testosterone significantly impairs libido even when total testosterone appears normal. 1
- Decreased libido is recognized as one of the most specific symptoms of hypogonadism 2
- Men with sexual symptoms of hypogonadism respond well to testosterone replacement therapy across a wide range of initial total testosterone values, including those with low-normal total testosterone levels 3
- In one study, 96.6% of men with total testosterone 201-300 ng/dL reported improvement in libido with treatment, compared to only 29.8% of those with total testosterone >301 ng/dL but low free testosterone 3
Orgasm Function
Testosterone therapy improves orgasmic function in hypogonadal men, including those with low free testosterone. 1
- Meta-analyses confirm that testosterone therapy significantly improves orgasm as measured by International Index of Erectile Function (IIEF) subscales 4
- Treatment options for orgasm problems (less intensity, difficulty achieving) include vibratory therapy, pelvic physical therapy, and PDE5 inhibitors, but testosterone therapy is indicated when morning testosterone is <300 ng/dL 1
- The NCCN guidelines specifically recommend testosterone therapy for problems with orgasm when total morning testosterone is low 1
Erectile Function
The relationship between low free testosterone and erectile function is more complex than with libido and orgasm. 1, 2, 4
- Testosterone therapy significantly improves erectile function (mean difference of 2.31 IIEF-EFD score points) compared to placebo in hypogonadal men 4
- Patients with more severe hypogonadism (total testosterone <8 nmol/L or approximately 231 ng/dL) show greater improvement than those with milder deficiency 4
- Cancer treatment can cause hypogonadism resulting in decreased libido and sexual function, which may respond to testosterone therapy 1
The Semen Expulsion Claim
The assertion that low free testosterone affects semen expulsion rather than production lacks strong clinical evidence.
- Testosterone is essential for spermatogenesis (production), and exogenous testosterone therapy actually suppresses sperm production in the short term and potentially long term 1, 5
- While testosterone therapy may improve ejaculatory function in hypogonadal men, the mechanism is not specifically related to "expulsion versus production" 1
- One study found no significant association between low total testosterone levels and semen parameters (volume, count, motility, morphology) in men with total sperm count >5 million 6
- The NCCN guidelines recommend testosterone therapy for ejaculatory problems when morning testosterone is <300 ng/dL, but do not distinguish between expulsion and production mechanisms 1
Clinical Algorithm for Assessment
When a patient presents with sexual symptoms:
Obtain morning (8-10 AM) total testosterone on two separate occasions 1, 5
Measure free testosterone by equilibrium dialysis or calculate using validated formulas incorporating total testosterone, SHBG, and albumin 1, 5
Document specific symptoms: reduced libido, erectile dysfunction, orgasm difficulties, ejaculatory problems, reduced energy, fatigue 1
If free testosterone is confirmed low on at least two assessments and symptoms are present, testosterone replacement therapy is indicated 1, 5
Measure luteinizing hormone and follicle-stimulating hormone to distinguish primary from secondary hypogonadism 1
Prior to treatment, measure hemoglobin/hematocrit and assess cardiovascular risk factors 5
Treatment Considerations
Testosterone replacement therapy should be considered when morning free testosterone by equilibrium dialysis is frankly low on at least two separate assessments. 1
- Transdermal preparations (gel, patch) provide stable day-to-day testosterone levels 1
- Intramuscular injections avoid daily administration but cause fluctuating levels 1
- Men interested in fertility should have reproductive health evaluation before starting testosterone therapy, as it suppresses spermatogenesis 1, 5
Critical Pitfalls
Do not rely on total testosterone alone in obese patients or those with altered SHBG levels - free testosterone measurement is mandatory. 1
Do not prescribe testosterone to men actively trying to conceive - exogenous testosterone suppresses sperm production. 1, 5
Do not assume all sexual dysfunction in men with low-normal total testosterone will respond to treatment - those with total testosterone >301 ng/dL but low free testosterone show variable response, with only 29.8% reporting libido improvement compared to 96.6% in those with total testosterone 201-300 ng/dL. 3
Recognize that sexual dysfunction has multifactorial causes - hypogonadism represents only one potential etiology, and vascular, psychological, and relational factors must be addressed concurrently. 2, 7