Confirming Biochemical Hypogonadism: Testosterone Testing Thresholds
To confirm biochemical hypogonadism in an adult male, you must obtain two separate morning total testosterone measurements (drawn between 8:00-10:00 AM) with both values below 300 ng/dL. 1, 2, 3
Diagnostic Threshold and Timing
- The diagnostic cutoff is <300 ng/dL for total testosterone on both measurements 1, 2, 3
- Morning timing (8:00-10:00 AM) is mandatory due to diurnal variation in testosterone production—afternoon or evening measurements will be physiologically lower and lead to false-positive diagnoses 4, 1, 2
- Two separate measurements are required because of natural day-to-day fluctuations and assay variability 1, 2, 3, 5, 6
- Use the same laboratory and methodology for both measurements to ensure consistency 2
Additional Testing Required for Borderline or Obese Patients
In men with total testosterone near the lower limit of normal (approximately 231-346 ng/dL) or in obese patients, you must measure free testosterone by equilibrium dialysis and sex hormone-binding globulin (SHBG). 4, 1, 2
- Obesity-related low total testosterone may be due solely to low SHBG with normal free testosterone—these men do not have true hypogonadism 4, 2
- However, a subset of obese men will have frankly low free testosterone levels due to increased aromatization of testosterone to estradiol in adipose tissue 4
- Free testosterone measurement is essential when total testosterone is borderline because low SHBG can artificially lower total testosterone while free testosterone remains normal 1, 2
Distinguishing Primary from Secondary Hypogonadism
Once low testosterone is confirmed on two occasions, measure serum LH and FSH to distinguish primary (testicular) from secondary (hypothalamic-pituitary) hypogonadism—this distinction is critical for treatment selection and fertility counseling. 1, 2, 3
- Elevated LH/FSH with low testosterone indicates primary (testicular) hypogonadism 1
- Low or low-normal LH/FSH with low testosterone indicates secondary (hypothalamic-pituitary) hypogonadism 1, 2
- Men with secondary hypogonadism who desire fertility should receive gonadotropin therapy (hCG plus FSH), not testosterone replacement, because testosterone causes azoospermia 1
Clinical Symptoms Required for Diagnosis
Biochemical confirmation alone is insufficient—diagnosis requires both low testosterone levels AND specific symptoms of hypogonadism. 1, 2, 3, 5, 6
Symptoms with proven benefit from testosterone therapy:
Symptoms with minimal or no proven benefit:
- Fatigue, low energy, or reduced physical function show little to no improvement with testosterone therapy (standardized mean difference 0.17) 1
- Depressive symptoms show less-than-small improvement (standardized mean difference -0.19) 1
- Cognition shows no benefit 1
Common Pitfalls to Avoid
- Never diagnose hypogonadism on a single testosterone measurement—two morning values are mandatory 1, 2, 3
- Never measure testosterone at random times of day—afternoon or evening measurements will be physiologically lower and lead to false-positive diagnoses 4, 2
- Never diagnose based on symptoms alone without biochemical confirmation—symptoms are nonspecific and overlap with many conditions 1, 2, 3
- Never omit LH/FSH testing once low testosterone is confirmed—the distinction between primary and secondary hypogonadism directs therapy and fertility counseling 1, 2
- Never use direct immunoassay measurements of free testosterone—use equilibrium dialysis or calculated values (Vermeulen formula) to ensure accuracy 1
Special Populations Requiring Testing
Even without symptoms, measure testosterone in men with: 2, 3
- Unexplained anemia
- Bone density loss or osteoporosis
- Type 2 diabetes
- HIV/AIDS
Target Levels During Treatment
If treatment is initiated, aim for testosterone levels in the mid-normal range (450-600 ng/dL or 350-750 ng/dL) during therapy. 1, 2