Is a total testosterone level of 337 ng/dL low in a 40‑year‑old male?

Is a Testosterone Level of 337 ng/dL Low in a 40-Year-Old Male?

A total testosterone of 337 ng/dL in a 40-year-old man falls into a diagnostic gray zone and does not definitively establish hypogonadism without additional testing and symptom assessment. This single value sits just above the widely accepted 300 ng/dL threshold but requires confirmation with a second early-morning measurement and correlation with specific clinical symptoms before any treatment decision can be made. 1

Understanding the Diagnostic Threshold

The American Urological Association defines testosterone deficiency as total testosterone < 300 ng/dL measured on two separate early-morning occasions (8–10 AM), combined with the presence of specific symptoms. 1 Your single value of 337 ng/dL places you in what guidelines call the "gray zone" (231–346 ng/dL), where clinical judgment and symptom assessment become critical. 2

Critical point: A single testosterone measurement is insufficient for diagnosis due to significant day-to-day variability and assay differences across laboratories. 1, 3 Nearly 25% of men receiving testosterone therapy do not actually meet diagnostic criteria when proper testing protocols are followed. 1

Age-Specific Considerations for a 40-Year-Old

Recent evidence suggests that the 300 ng/dL cutoff may not be appropriate for younger men. In men aged 40–44 years, the middle tertile (normal range) is 350–473 ng/dL, with the lower cutoff for this age group being 350 ng/dL. 4 By this age-specific standard, your level of 337 ng/dL would be considered low-normal to borderline low.

However, the Princeton III Consensus and multiple international societies agree that testosterone > 350 ng/dL typically does not require replacement therapy unless specific symptoms are present. 5

Required Next Steps for Diagnosis

1. Confirm with Repeat Morning Testing

• Obtain a second fasting morning total testosterone measurement between 8–10 AM on a separate day. 1, 2
• Both measurements must be < 300 ng/dL to establish biochemical hypogonadism by AUA criteria. 1
• Morning timing is mandatory because testosterone peaks between 8 AM and 10 AM; afternoon measurements risk false-positive diagnoses. 1

2. Assess for Qualifying Symptoms

Diagnosis requires both low testosterone AND specific symptoms. 1 The symptoms with the strongest evidence for testosterone-responsive improvement are:

• Diminished libido (decreased sex drive) 1, 6
• Erectile dysfunction (difficulty achieving or maintaining erections) 1
• Decreased spontaneous or morning erections 7

Important: Nonspecific symptoms like fatigue, low energy, depressed mood, poor concentration, and reduced physical strength show little to no correlation with testosterone levels and demonstrate minimal to no improvement with testosterone therapy. 7, 6 In a large preventive medicine cohort, fatigue, depression, and erectile dysfunction were not associated with low testosterone levels (p > 0.6). 6

3. Additional Laboratory Testing (If Repeat Testosterone Confirms Low Levels)

If your second morning testosterone is also < 300 ng/dL, the following tests are mandatory:

• LH and FSH to distinguish primary (testicular) from secondary (pituitary-hypothalamic) hypogonadism 1
• Free testosterone by equilibrium dialysis (especially important at borderline levels or if you have obesity/diabetes) 1
• Sex hormone-binding globulin (SHBG) to calculate free androgen index 1
• Prolactin (if LH/FSH are low-normal) 1
• Fasting glucose and HbA1c (metabolic syndrome is associated with low testosterone) 1

Treatment Decision Algorithm

If both morning testosterone measurements are < 300 ng/dL AND you have diminished libido or erectile dysfunction:

• You meet diagnostic criteria for hypogonadism and may be a candidate for testosterone therapy. 1
• Expected benefit: small but significant improvement in sexual function (standardized mean difference 0.35). 7, 1
• Little to no benefit for energy, physical function, mood, or cognition. 7

If testosterone is 300–350 ng/dL (gray zone) AND you have sexual symptoms:

• A 4–6 month therapeutic trial may be considered after careful risk-benefit discussion. 2
• Reevaluate at 12 months; discontinue if no improvement in sexual function. 1

If testosterone is > 350 ng/dL:

• Testosterone replacement is not indicated, regardless of symptoms. 5

If your primary complaints are fatigue, low energy, or mood issues without sexual symptoms:

• Testosterone therapy is not recommended even with confirmed low testosterone, as evidence shows minimal to no benefit for these symptoms. 7, 6

Common Pitfalls to Avoid

• Do not diagnose hypogonadism on a single measurement. 1, 3
• Do not test outside of morning hours (8–10 AM). 1, 2
• Do not rely on symptoms alone without biochemical confirmation. 1
• Do not expect testosterone to improve fatigue, energy, or mood—these symptoms show no correlation with testosterone levels and minimal response to therapy. 7, 6
• Do not ignore free testosterone assessment if total testosterone is borderline or if you have obesity. 1

Bottom Line

Your testosterone level of 337 ng/dL is borderline low for your age but does not establish a diagnosis without a confirmatory second early-morning measurement and assessment of specific sexual symptoms (diminished libido or erectile dysfunction). If you are experiencing primarily fatigue, low energy, or mood issues without sexual symptoms, testosterone therapy is unlikely to provide meaningful benefit even if repeat testing confirms low levels. 7, 6