What are normal levels of testosterone (testosterone) in adults?

Normal Testosterone Levels in Adults

Normal testosterone levels in adults vary by age, with a threshold of 300 ng/dL generally considered the lower limit for diagnosis of testosterone deficiency in men, though age-specific reference ranges should be used when available, particularly for younger men who typically have higher baseline levels.

Reference Ranges for Total Testosterone

Age-Specific Normal Ranges

• Men in their 40s: 8.7-31.7 nmol/L (251-914 ng/dL) 1
• Men in their 50s: 7.5-30.4 nmol/L (216-876 ng/dL) 1
• Men in their 60s: 6.8-29.8 nmol/L (196-859 ng/dL) 1
• Men in their 70s: 5.4-28.4 nmol/L (156-818 ng/dL) 1

Younger Men (20-44 years)

More recent research suggests higher reference ranges for younger men 2:

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

Diagnostic Threshold

The American Urological Association (AUA) recommends using a total testosterone level below 300 ng/dL as a reasonable cut-off to support the diagnosis of low testosterone 3.

Gender Differences

There is a clear bimodal distribution of testosterone levels between males and females 4:

• Males: 8.8-30.9 nmol/L (254-891 ng/dL)
• Females: 0.4-2.0 nmol/L (12-58 ng/dL)

Important Considerations for Testing

Proper Testing Protocol

1. Multiple measurements required: The diagnosis of low testosterone should only be made after two total testosterone measurements are taken on separate occasions 3
2. Morning testing: Both measurements should be conducted in an early morning fashion (between 8-10 AM) when testosterone levels are typically highest 3, 5
3. Consistent laboratory: Preferably using the same laboratory with the same method/instrumentation for measurement 3

Factors Affecting Testosterone Levels

Several factors can influence testosterone levels and should be considered when interpreting results:

• Health status: Chronic disease, medications, and obesity can significantly decrease testosterone levels 1
• BMI: Higher BMI is associated with lower testosterone levels 1
• Smoking: Tends to increase total, free, and bioavailable testosterone concentrations 1
• Alcohol consumption: Excessive alcohol can affect hormone levels 1

Free and Bioavailable Testosterone

In certain clinical scenarios, measurement of free or bioavailable testosterone may be helpful:

• Free testosterone: Should be measured by equilibrium dialysis when total testosterone levels are borderline or when conditions affecting sex hormone-binding globulin (SHBG) are present 5
• Normal range for free testosterone: 70.0-141.8 pg/mL (based on 2.5th percentile to mean) 6

Clinical Implications

When evaluating testosterone levels, it's important to consider both laboratory values and clinical symptoms:

• The clinical diagnosis of testosterone deficiency should only be made when patients have low total testosterone levels combined with symptoms and/or signs 3
• Target testosterone levels for patients on replacement therapy should be in the mid-normal range, approximately 450-600 ng/dL 5

Common Pitfalls in Testosterone Testing

1. Single measurements: Relying on a single testosterone measurement instead of two separate morning measurements
2. Afternoon testing: Testosterone levels naturally decline throughout the day
3. Not considering age: Using the same reference range for all adult men regardless of age
4. Ignoring symptoms: Diagnosing based solely on laboratory values without considering clinical symptoms
5. Not accounting for health factors: Failing to consider how obesity, medications, and chronic diseases affect testosterone levels

By understanding normal testosterone ranges and following proper testing protocols, clinicians can more accurately diagnose testosterone deficiency and monitor treatment effectiveness.