What is a normal free testosterone level in an adult male patient with suspected hypogonadism?

Normal Free Testosterone Levels in Adult Males

Normal free testosterone levels in adult males typically range from approximately 63 pg/mL and above, though the diagnosis of hypogonadism requires both biochemical confirmation with total testosterone below 300 ng/dL on two separate morning measurements AND the presence of specific symptoms, particularly diminished libido and erectile dysfunction. 1, 2, 3

Diagnostic Thresholds and Reference Ranges

Total testosterone is the primary screening test, with the following thresholds guiding clinical decision-making:

• Below 300 ng/dL (10.4 nmol/L): Supports diagnosis of hypogonadism when measured on two separate mornings 1, 2, 3
• 300-350 ng/dL: Gray zone requiring free testosterone measurement, as total testosterone in this range has insufficient sensitivity (91.0%) to exclude hypogonadism 4
• Above 350-400 ng/dL: Reliably predicts normal free testosterone and typically does not require replacement therapy 4, 2

Free testosterone becomes essential when total testosterone is borderline or when conditions affecting sex hormone-binding globulin (SHBG) are present, particularly obesity or diabetes 1, 3:

• Below 63 pg/mL: Indicates hypogonadism 5
• Normal range: Approximately 63 pg/mL and above 5

Critical Measurement Requirements

Both measurements must be obtained correctly to avoid misdiagnosis:

• Draw blood between 8-10 AM on two separate occasions to confirm persistent hypogonadism, as single measurements are insufficient due to diurnal variation and assay variability 1, 6
• Fasting morning samples provide the most accurate assessment 3
• Free testosterone should be measured by equilibrium dialysis when total testosterone is borderline (280-350 ng/dL), as this is the gold standard method 1

When Free Testosterone Measurement is Essential

Free testosterone assessment is mandatory in specific clinical scenarios where total testosterone may be misleading:

• Obesity: Low SHBG artificially lowers total testosterone while free testosterone remains normal 1, 3
• Diabetes: SHBG abnormalities are common 1
• Total testosterone 280-350 ng/dL: This range misses hypogonadism in 8.4% of men with sexual symptoms when relying on total testosterone alone 5
• Borderline total testosterone with symptoms: Only 24.7% of men with borderline total testosterone actually have confirmed hypogonadism by free testosterone 5

Clinical Context: Symptoms Matter

Biochemical thresholds alone do not justify treatment—specific symptoms must be present:

• Primary symptoms warranting evaluation: Diminished libido, decreased spontaneous erections, erectile dysfunction 1, 7
• Secondary symptoms with weaker evidence: Decreased physical stamina, depressed mood, fatigue, increased visceral adiposity 7
• Minimal or no benefit expected: Physical functioning, energy/vitality, cognition—testosterone therapy produces little to no meaningful improvement in these domains even with confirmed hypogonadism 1

Common Diagnostic Pitfalls

Avoid these critical errors that lead to inappropriate diagnosis and treatment:

• Never diagnose hypogonadism on a single testosterone measurement: Two separate morning measurements are required 1, 6
• Do not rely solely on total testosterone in the 280-350 ng/dL range: This misses 8.4% of true hypogonadism cases 5
• Recognize that 20-25% of men receiving testosterone therapy do not meet diagnostic criteria: Many are inappropriately treated without confirmed low testosterone 1, 3
• Laboratory reference ranges vary by 350% between facilities: The lower limit ranges from 130-450 ng/dL across different labs, making standardized thresholds critical 8
• Age-related decline is not automatically pathologic: Testosterone naturally decreases with age, but this does not constitute disease requiring treatment unless specific symptoms are present 2

Distinguishing Primary from Secondary Hypogonadism

After confirming low testosterone, measure LH and FSH to determine the type:

• Elevated LH/FSH with low testosterone: Primary (testicular) hypogonadism 1
• Low or low-normal LH/FSH with low testosterone: Secondary (hypothalamic-pituitary) hypogonadism 1
• This distinction has critical treatment implications: Men with secondary hypogonadism desiring fertility require gonadotropin therapy (hCG plus FSH), as testosterone replacement causes azoospermia 1

Special Population Considerations

Free testosterone correlates better with clinical parameters than total testosterone:

• Free testosterone significantly associates with age, hematocrit, gonadotropins, gynecomastia, BMI, number of comorbidities, erectile dysfunction, and low libido 5
• Total testosterone associates only with BMI and low libido 5
• In men with sexual symptoms, routine free testosterone assessment improves diagnostic accuracy by identifying 25% with hypogonadism who would be missed by total testosterone alone 5