What are the normal values of testosterone in adult males?

Normal Testosterone Values in Adult Males

The normal range for testosterone in adult men is generally considered to be 300-800 ng/dL in most laboratories. 1, 2

Reference Ranges

• The American Urological Association defines a testosterone level below 300 ng/dL as a reasonable cut-off to support the diagnosis of low testosterone across all adult age groups 2
• Laboratory reference ranges for testosterone vary significantly among testing facilities, with the mean lower reference value being 231 ± 46 ng/dL (range 160-300) and the mean upper limit being 850 ± 141 ng/dL (range 726-1,130) 3
• For men on testosterone therapy, the target trough testosterone level should be maintained within the physiological range of 300-1,000 ng/dL 4

Age-Specific Considerations

• Testosterone levels naturally decline with age, suggesting the need for age-specific reference ranges 5
• Recent research suggests that young men (20-44 years) have different testosterone reference ranges than older men, with age-specific cutoffs for low testosterone being higher in younger men 6:
  • 20-24 years: 409 ng/dL
  • 25-29 years: 413 ng/dL
  • 30-34 years: 359 ng/dL
  • 35-39 years: 352 ng/dL
  • 40-44 years: 350 ng/dL 6
• For men in their 40s, 50s, 60s, and 70s, the 95% reference ranges (2.5-97.5th percentile) in apparently healthy men are:
  • 40s: 251-914 ng/dL
  • 50s: 216-876 ng/dL
  • 60s: 196-859 ng/dL
  • 70s: 156-818 ng/dL 5

Measurement Considerations

• The diagnosis of low testosterone should only be made after two total testosterone measurements are taken on separate occasions, both conducted in an early morning fashion 2
• Morning measurements are critical as testosterone levels naturally fluctuate throughout the day, with highest levels typically occurring in the morning 2, 7
• Sampling for the estimation of plasma testosterone should be carried out in the morning, before 11:00 am, to account for the marked diurnal variation in testosterone production 7
• When total testosterone levels are borderline (280-350 ng/dL), free testosterone assessment should be considered 8
• Total testosterone must exceed 350-400 ng/dL to reliably predict normal free testosterone 8

Clinical Implications of Testosterone Levels

• Testosterone deficiency in males is associated with energy imbalance, impaired glucose control, reduced insulin sensitivity, dyslipidemia, increased abdominal fat mass, and reduced lean body mass 1, 2
• When evaluating low total testosterone clinically in a man with obesity, measurement of morning serum free testosterone is essential, as obesity can affect sex hormone-binding globulin levels 1, 2
• Low testosterone levels can affect sexual function, with studies showing that testosterone treatment improves sexual function in men with low levels 2

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 2
• Nearly half of men placed on testosterone therapy do not have their testosterone levels checked after therapy commences 2
• Only 9% of laboratories where in-house total testosterone testing is performed create a reference range unique to their region, which may affect diagnostic accuracy 3
• When testosterone levels are found to be around the lower limit of normal (approximately 9.0 nmol/L or 260 ng/dL), some measure of bioactive testosterone (free or bioavailable) should be sought 7

By understanding normal testosterone ranges and proper measurement techniques, clinicians can more accurately diagnose and treat testosterone abnormalities in adult males, ultimately improving patient outcomes related to morbidity, mortality, and quality of life.