Total testosterone 400 - should I start TRT?

Two guidelines set the reference points most clinicians use. The Endocrine Society 2018 guideline anchors diagnosis to a harmonized reference range - established across four cohorts and standardized to the CDC reference method - whose lower limit in healthy nonobese men aged 19 to 39 is 264 ng/dL (the range is 264 to 916 ng/dL). The AUA guideline states that clinicians should use a total testosterone below 300 ng/dL as a reasonable cut-off in support of a low-testosterone diagnosis.

A reading of 400 ng/dL is above both. In the language the guidelines use, it is not unequivocally low. That does not settle anything by itself - it means the number alone does not meet the threshold that guidelines treat as supporting a diagnosis.

Both guidelines are explicit that a low reading is one half of a diagnosis, never the whole of it. The Endocrine Society recommends diagnosing hypogonadism only in men who have symptoms and signs consistent with testosterone deficiency AND unequivocally and consistently low serum testosterone. The AUA frames the same idea from the other side: the clinical diagnosis is made only when low total testosterone occurs together with symptoms and/or signs.

So the framework has two gates, not one. Symptoms without a low confirmed level do not meet it; a low level without symptoms does not meet it either. At 400 ng/dL the level gate is not crossed on the numbers the guidelines cite, whatever the symptom picture looks like.

Testosterone peaks in the morning and falls through the day, and any single draw also carries assay and day-to-day biological variation. Both guidelines build that into the diagnostic rule. The Endocrine Society specifies fasting, morning measurement and confirmation of a low value by repeating it. The AUA is more specific still: the diagnosis should be made only after two total testosterone measurements taken on separate occasions, both drawn in an early-morning fashion.

A 400 measured in the afternoon, or a 400 that has never been repeated, is a snapshot rather than a confirmed value. The guideline procedure - repeat on a separate morning - exists precisely because one reading can land higher or lower than a person's typical level.

Total testosterone can be misleading when SHBG, the protein that binds most circulating testosterone, is unusually high or low. The Endocrine Society advises measuring free testosterone in men whose total is near the lower limit or who have a condition that shifts SHBG - obesity, insulin resistance, thyroid disease, and others. Low SHBG lowers total testosterone while raising the free fraction, so a total near or above 400 can read differently once free testosterone is calculated.

If SHBG is on your panel, our free testosterone calculator estimates free T from total T, SHBG, and albumin. See what low SHBG means for how the binding protein reshapes these numbers.

Testosterone is a Schedule III controlled substance, and whether to start therapy is a decision for you and a licensed clinician who can weigh your full history. This page reports the decision framework the guidelines describe - the thresholds, the symptom requirement, the repeat morning test, the role of free testosterone - so you can read your own result against what the guidelines actually say. It does not recommend starting or not starting TRT, and it is not a substitute for a physician's evaluation.