For adult men, testosterone replacement therapy (TRT) is generally considered when total testosterone is below 300 ng/dL (10.4 nmol/L) on two separate early-morning tests and the man has symptoms or signs of testosterone deficiency. A result below 300 ng/dL alone does not mean TRT should start. A 2026 Endocrine Society statement also identifies weight loss as typical first-line treatment when obesity is the likely cause of low testosterone and no other cause has been found.
Testosterone Levels and How Doctors Interpret Them
| Total testosterone result | Usual clinical interpretation |
|---|---|
| Below 264 ng/dL | Below the Endocrine Society's CDC-harmonized lower limit for standardized assays. Symptoms, repeat testing and the cause of the low result still need evaluation. |
| 264 to 299 ng/dL | Borderline to low. The American Urological Association uses below 300 ng/dL as a reasonable cutoff, but TRT generally also requires compatible symptoms and a second low result. |
| 300 to 400 ng/dL | TRT is not usually recommended based on total testosterone alone. A clinician may check free testosterone, especially when symptoms are present or sex hormone-binding globulin may be abnormal. |
| Above 400 ng/dL | Low testosterone is less likely, although the result may still need to be considered alongside symptoms, free testosterone and the laboratory's reference range. |
The 300 ng/dL threshold is a practical cutoff, not a universal treatment trigger. The Endocrine Society looks for testosterone that is "unequivocally and consistently low." The American Urological Association combines a low testosterone result with symptoms or signs before making the diagnosis.
What Must Be True Before TRT Is Recommended?
Doctors usually look for all or most of the following:
- Symptoms or signs of testosterone deficiency, such as reduced libido, erectile problems, fewer spontaneous erections, loss of muscle mass or unexplained anemia.
- Two low testosterone results taken on separate days.
- Early-morning testing, usually before 10 a.m., because testosterone levels change during the day.
- Accurate testing, ideally through a reliable laboratory assay.
- An assessment of the cause, including medication effects, obesity, pituitary disorders and testicular disease.
An acute illness can temporarily lower testosterone. In that situation, a clinician may repeat the test after recovery instead of starting TRT immediately.
When Is Free Testosterone Important?
Free testosterone can help when total testosterone is near the lower limit, commonly around 200 to 400 ng/dL, or when a condition may change sex hormone-binding globulin levels. Relevant conditions include obesity, aging, liver disease, thyroid disorders and certain medications.
For example, a man with total testosterone around 280 ng/dL and a low free testosterone result may have stronger evidence of testosterone deficiency than a man with the same total testosterone but normal free testosterone. The result still needs to be interpreted according to the test method and the laboratory's reference range.
What Happens After a Confirmed Low Result?
Doctors usually order more tests, including luteinizing hormone and follicle-stimulating hormone. These help distinguish testicular failure from a problem involving the pituitary gland or hypothalamus. Treatment may differ depending on the cause.
TRT may be reasonable for a man who has:
- Repeated morning testosterone below approximately 300 ng/dL
- Consistent symptoms or signs of testosterone deficiency
- No untreated reversible cause
- No major contraindication to treatment
- A plan to monitor testosterone, hematocrit and prostate-related risk
When TRT May Not Be Appropriate
TRT should not be started simply because one test shows a low result.
The Endocrine Society recommends against TRT in men planning fertility in the near term because external testosterone can suppress sperm production. Other concerns include:
- Elevated hematocrit
- Untreated severe sleep apnea
- Prostate or breast cancer
- Certain prostate findings
- Uncontrolled heart failure
- A recent heart attack or stroke
- Thrombophilia
When obesity appears to be the main cause of low testosterone, a clinician may recommend weight loss and treatment of other reversible factors first. The Endocrine Society's 2026 statement identifies weight loss as typical first-line treatment when obesity is the likely cause and no other cause has been found.
Bottom Line
The testosterone number starts the evaluation, but it does not decide the treatment by itself. Doctors generally look for symptoms, two separate low morning results, a clear assessment of the cause and no major safety concern.
A single low testosterone result should lead to confirmation and further evaluation, not an automatic TRT prescription.