Understanding Your Testosterone Level
To determine how low you are on the testosterone scale, you need two separate morning testosterone measurements (between 8-10 AM), with levels below 300 ng/dL indicating testosterone deficiency according to the American Urological Association. 1
Diagnostic Thresholds
The testosterone scale is defined by specific cut-offs that guide clinical decision-making:
- Below 300 ng/dL: This is the established threshold for low testosterone (hypogonadism) in adult men 1
- 300-1000 ng/dL: This represents the normal adult male range 1
- 350-750 ng/dL: This mid-normal range is often targeted during testosterone replacement therapy 1
A single measurement is insufficient for diagnosis—you must have two separate morning measurements both showing levels below 300 ng/dL to confirm testosterone deficiency. 1
Critical Measurement Requirements
To accurately assess where you fall on the testosterone scale:
- Timing matters: Blood must be drawn between 8 AM and 10 AM due to diurnal variation in testosterone production, with levels being highest in the early morning 1, 2
- Repeat testing is mandatory: Natural fluctuations in testosterone levels mean a single low value could be misleading 1
- Total testosterone is the initial test: This should be measured using a reliable assay as your first diagnostic step 3
When Additional Testing Is Needed
If your total testosterone falls in the equivocal range (approximately 300-350 ng/dL), you may need:
- Free or bioavailable testosterone measurement: This clarifies the diagnosis when total testosterone is near the lower limit of normal 1, 4
- These tests are particularly important if you have conditions affecting sex hormone-binding globulin (SHBG), such as obesity, which can alter the interpretation of total testosterone 3
Individual Variation in Testosterone Thresholds
Research shows that each person has a consistent but individual testosterone threshold for experiencing deficiency symptoms, which can vary markedly between men. 5 The symptomatic threshold ranges widely:
- Men with secondary hypogonadism (pituitary/hypothalamic origin) typically experience symptoms at lower levels (around 9.7 nmol/L or approximately 280 ng/dL) 5
- Men with primary hypogonadism (testicular origin) may not experience symptoms until levels reach 11.7 nmol/L (approximately 337 ng/dL) 5
Clinical Context Is Essential
Diagnosis requires both low testosterone levels AND symptoms of hypogonadism—laboratory values alone are insufficient. 1 Common symptoms include:
- Reduced energy and fatigue 1, 6
- Decreased libido and erectile dysfunction 6, 5
- Reduced motivation and concentration 6
- Depression 1, 6
- Decreased muscle mass and strength 3
Common Pitfalls to Avoid
- Never rely on a single testosterone measurement: This is the most common diagnostic error 1
- Don't diagnose based solely on lab values: Symptoms must be present to justify treatment 1
- Avoid afternoon or evening testing: Testosterone levels decline throughout the day, leading to falsely low results 1, 2
- Be aware of laboratory variability: Reference ranges vary widely between labs (low values ranging from 130-450 ng/dL across different laboratories), so the 300 ng/dL threshold provides standardization 7
Special Considerations for Adolescents
If you are 15 years old or younger, the adult cutoff of 300 ng/dL does not apply—age-appropriate norms are likely higher (above 350 ng/dL based on young adult data). 2 Adolescents with persistently low testosterone warrant referral to a pediatric endocrinologist 2.