Appropriate Testosterone Testing for Erectile Dysfunction
For men with erectile dysfunction, bioavailable or free testosterone testing is preferred over total testosterone, especially in obese patients or those with conditions affecting sex hormone-binding globulin (SHBG). 1
Recommended Testosterone Testing Protocol
Initial Testing
- Measure morning total testosterone levels (between 8-10 AM when levels are highest)
- Include free or bioavailable testosterone measurement, particularly in:
- Obese patients
- Patients with conditions affecting SHBG
- Patients with borderline total testosterone results
Confirmatory Testing
- Repeat morning testosterone measurement to confirm initial findings
- Include SHBG measurement to accurately assess testosterone bioavailability
- Add luteinizing hormone (LH) testing to distinguish between primary and secondary hypogonadism
Essential Laboratory Panel for ED Evaluation
- Morning total testosterone (essential)
- Free or bioavailable testosterone (preferred in specific populations)
- Sex hormone-binding globulin (SHBG)
- Luteinizing hormone (LH)
- HbA1c
- Fasting blood glucose
- Lipid profile
Interpretation of Results
- Normal total testosterone range: 300-800 ng/dL 1
- Consider hypogonadism if:
- Total testosterone <300 ng/dL on two separate measurements
- Free testosterone is low despite normal total testosterone (common with high SHBG)
- Free testosterone index (total testosterone/SHBG ratio) <0.3
Clinical Relevance
- Testosterone deficiency is associated with declining erectile function, with levels inversely correlated with ED severity 2
- Up to 15% of males with erectile dysfunction show diminished testosterone levels 3
- Testosterone plays essential roles in erectile physiology at both central and peripheral levels 2
- Testosterone increases expression of nitric oxide synthase and phosphodiesterase type 5, key enzymes in the erectile process 2
Treatment Implications
- Testosterone replacement therapy can restore erectile function in hypogonadal men 2
- A significant proportion of PDE5 inhibitor non-responders are testosterone deficient 2
- Testosterone replacement can convert over half of PDE5 inhibitor non-responders into responders 2, 4
- Combined therapy (testosterone plus PDE5 inhibitors) may be effective when monotherapy fails 3, 4
Common Pitfalls to Avoid
- Relying solely on total testosterone without measuring free/bioavailable testosterone, especially in obese patients
- Failing to repeat testosterone measurements to confirm hypogonadism
- Not measuring SHBG, which affects testosterone bioavailability
- Overlooking secondary causes of hypogonadism (pituitary disorders)
- Testing at inconsistent times of day (levels fluctuate throughout the day)
- Not considering testosterone testing in PDE5 inhibitor non-responders
Special Considerations
- Target mid-normal range (350-600 ng/dL) for testosterone replacement therapy
- Monitor for adverse effects of testosterone therapy (polycythemia, prostate issues)
- Contraindications for testosterone therapy include prostate/breast cancer and desire for fertility
- Consider estradiol levels if breast symptoms or gynecomastia are present