What are normal testosterone levels and when should testing be done?

Normal Testosterone Levels and Testing Timing

The diagnosis of low testosterone requires a total testosterone level below 300 ng/dL measured on two separate early morning (8-10 AM) blood draws, combined with clinical symptoms of hypogonadism. 1

Normal Testosterone Reference Ranges

Adult men typically have testosterone levels between 300-800 ng/dL in most laboratories, though significant variability exists across testing facilities. 1, 2

Age-Specific Considerations

While the 300 ng/dL cutoff applies across all adult age groups per AUA guidelines 1, younger men naturally have higher baseline levels:

• Ages 20-24: Middle tertile range 409-558 ng/dL 3
• Ages 25-29: Middle tertile range 413-575 ng/dL 3
• Ages 30-34: Middle tertile range 359-498 ng/dL 3
• Ages 35-39: Middle tertile range 352-478 ng/dL 3
• Ages 40-44: Middle tertile range 350-473 ng/dL 3

For young men (20-44 years), age-specific cutoffs ranging from 350-413 ng/dL may be more appropriate than the universal 300 ng/dL threshold, as this population has higher baseline testosterone production. 3

When to Test Testosterone

Timing Requirements

Both testosterone measurements must be obtained between 8 AM and 10 AM on separate days, as testosterone levels peak in early morning and decline throughout the day. 1 This timing is critical for diagnostic accuracy.

Fasting morning samples provide the most accurate assessment. 4

Clinical Indications for Testing

Test testosterone in men presenting with symptoms of hypogonadism including:

• Reduced libido and decreased spontaneous erections 4
• Erectile dysfunction 4
• Decreased physical stamina, strength, and muscle mass 4
• Fatigue and reduced energy 1
• Depressed mood 4
• Increased visceral adiposity 4
• Sleep disturbance and poor concentration/memory 4

Also test asymptomatic men with specific medical conditions: unexplained anemia, bone density loss, diabetes, chemotherapy or testicular radiation exposure, HIV/AIDS, chronic narcotic use, male infertility, pituitary dysfunction, or chronic corticosteroid use. 1

Diagnostic Algorithm

Initial Testing

1. Measure total testosterone on two separate mornings between 8-10 AM 1
2. If both values are <300 ng/dL AND symptoms are present, diagnose testosterone deficiency 1
3. In obese men with low total testosterone, also measure free testosterone by equilibrium dialysis and sex hormone-binding globulin, as obesity can lower sex hormone-binding globulin while free testosterone remains normal 1

Confirmatory Testing

If testosterone levels are subnormal on repeat testing, measure luteinizing hormone and follicle-stimulating hormone to distinguish primary (testicular) from secondary (pituitary-hypothalamic) hypogonadism. 1

For secondary hypogonadism (low testosterone with low LH/FSH), further evaluation includes serum prolactin, iron saturation, pituitary function testing, and MRI of the sella turcica. 1

Critical Thresholds for Clinical Decision-Making

Total testosterone >350 ng/dL typically does not require replacement therapy. 4

Total testosterone <230 ng/dL usually benefits from testosterone replacement in symptomatic men. 4

Total testosterone 231-346 ng/dL represents a gray zone where a 4-6 month trial may be considered in symptomatic men after careful risk-benefit discussion. 4

Total testosterone must exceed 350-400 ng/dL to reliably predict normal free testosterone levels, meaning values between 280-350 ng/dL are not sensitive enough to exclude hypogonadism. 5

Common Pitfalls to Avoid

Do not diagnose testosterone deficiency based on a single random testosterone measurement - this is inadequate for diagnosis. 1, 4

Do not test testosterone in the afternoon or evening - levels naturally decline throughout the day, leading to false-positive results. 1

Do not initiate treatment without confirming symptoms - approximately 25% of men receiving testosterone therapy do not meet diagnostic criteria for testosterone deficiency. 1, 4

In obese men, do not rely solely on total testosterone - measure free testosterone by equilibrium dialysis, as low sex hormone-binding globulin can falsely lower total testosterone while free testosterone remains normal. 1

Be aware that laboratory reference ranges vary dramatically - the lower limit ranges from 130-450 ng/dL across different laboratories (a 350% difference), which significantly affects clinical decision-making. 2, 6