What are normal testosterone levels?

Normal Testosterone Levels in Adult Males

The normal range for testosterone in adult men is generally considered to be 300-800 ng/dL in most laboratories, with the American Urological Association defining a level below 300 ng/dL as a reasonable cut-off to support the diagnosis of low testosterone. 1

Reference Ranges by Age

• Adult reference ranges typically define 300 ng/dL as the lower threshold for normal testosterone levels, though this cutoff was primarily developed from samples of older men 2
• Age-specific middle tertile levels for younger men are higher than the standard 300 ng/dL cutoff:
  • 20-24 years: 409-558 ng/dL (cutoff: 409 ng/dL)
  • 25-29 years: 413-575 ng/dL (cutoff: 413 ng/dL)
  • 30-34 years: 359-498 ng/dL (cutoff: 359 ng/dL)
  • 35-39 years: 352-478 ng/dL (cutoff: 352 ng/dL)
  • 40-44 years: 350-473 ng/dL (cutoff: 350 ng/dL) 3
• For men in their 40s through 70s, the expected total testosterone ranges (2.5th-97.5th percentile) are:
  • 40s: 8.7-31.7 nmol/L (251-914 ng/dL)
  • 50s: 7.5-30.4 nmol/L (216-876 ng/dL)
  • 60s: 6.8-29.8 nmol/L (196-859 ng/dL)
  • 70s: 5.4-28.4 nmol/L (156-818 ng/dL) 4

Measurement Considerations

• The diagnosis of low testosterone should only be made after two total testosterone measurements taken on separate occasions, both conducted in the early morning 1
• Morning measurements (between 8 AM and 10 AM) are critical as testosterone levels naturally fluctuate throughout the day, with highest levels typically occurring in the morning 1, 2
• Fasting morning testosterone levels provide the most accurate assessment 1
• Many clinical laboratories now employ liquid chromatography tandem mass spectrometry (LC-MS/MS), which provides more accurate measurements, especially at lower concentration ranges 5

Clinical Implications of Testosterone Levels

• Low testosterone levels are associated with:
  • Energy imbalance
  • Impaired glucose control
  • Reduced insulin sensitivity
  • Dyslipidemia
  • Increased abdominal fat mass
  • Reduced lean body mass 1
• Men with low testosterone are more likely to experience:
  • Sexual dysfunction
  • Physical dysfunction (slow walking speed, difficulty climbing stairs, frailty)
  • Diabetes 6

Common Pitfalls in Testosterone Assessment

• Many men receive testosterone therapy without proper diagnosis - studies estimate that up to 25% of men who receive testosterone therapy do not meet the criteria to be diagnosed as testosterone deficient 1
• Nearly half of men placed on testosterone therapy do not have their testosterone levels checked after therapy commences 1
• When evaluating low total testosterone in a man with obesity, measurement of morning serum free testosterone is essential, as obesity can affect sex hormone-binding globulin levels 1
• Single measurements may be misleading due to significant intra-individual variability; at least two measurements should be obtained, especially for equivocal results (7.0-12.5 nmol/L or approximately 200-360 ng/dL) 7

Monitoring Testosterone Therapy

• For men on testosterone therapy, the target trough testosterone level should be maintained within the physiological range of 300-1,000 ng/dL 1
• Long-term efficacy and safety of testosterone therapy in men without well-established medical conditions known to cause hypogonadism are unknown 8