Normal FSH/Testosterone Ratio
The normal free testosterone index (total testosterone/SHBG ratio) should be >0.3, with normal FSH levels ranging between 1.5-8 mIU/ml in men. 1, 2
Normal Reference Ranges
FSH Normal Values
- Normal FSH range: 1.5-8 mIU/ml 2
- FSH levels <12 IU/L often indicate normal spermatogenesis 2
- However, recent evidence suggests that FSH levels >4.5 IU/L may be associated with abnormal semen parameters 3
Testosterone and Ratio Values
- Free testosterone index (total testosterone/SHBG ratio) should be >0.3 1
- A ratio <0.3 indicates hypogonadism 1
- Morning blood draws are essential for accurate testosterone measurement due to significant diurnal variation 1
Clinical Significance of FSH/Testosterone Ratio
Interpretation in Male Fertility Assessment
- FSH levels correlate negatively with spermatogenesis - higher FSH generally indicates poorer sperm production 2, 3
- Men with FSH levels >7.5 IU/L have five to thirteen times higher risk of abnormal semen quality compared to men with FSH <2.8 IU/L 3
- Decreasing testosterone/FSH ratios correlate with increasing probability of abnormal semen parameters 3
Hypogonadism Assessment
- Primary hypogonadism: Low testosterone, elevated LH and FSH 1
- Secondary hypogonadism: Low testosterone with normal or reduced LH and FSH 1
- Adult-onset hypogonadism: Low testosterone with normal or low gonadotropins 1
Important Considerations
Testing Recommendations
- Morning blood draws are essential for testosterone measurement due to diurnal variation 1
- When assessing male fertility, both FSH and testosterone should be measured together 2, 3
- SHBG measurement is important when interpreting total testosterone levels, especially in patients with liver disease where SHBG may be elevated 1
Common Pitfalls
- Relying solely on total testosterone without considering SHBG levels can lead to misdiagnosis, especially in patients with liver disease 1
- Using outdated reference ranges - evidence suggests traditional "normal" FSH ranges may need reconsideration 3
- Failure to consider time of day for testosterone measurement can lead to falsely low readings 1
- Not recognizing that normal FSH levels don't always guarantee normal spermatogenesis (some men with maturation arrest can have normal FSH despite severe spermatogenic dysfunction) 2
The relationship between FSH and testosterone is complex, with both hormones playing crucial and complementary roles in male reproductive function. The testosterone/FSH ratio provides valuable information about testicular function and spermatogenesis potential beyond what either hormone alone can indicate.