Verbatim response from Perplexity
A total testosterone below 300 ng/dL is the most common cutoff used to define low testosterone in adult men, but treatment is usually recommended only when low levels are confirmed on repeat morning blood tests and you have symptoms such as low libido, fatigue, or erectile dysfunction[4][6][2].
A few important nuances:
- 300 ng/dL is the widely used diagnostic threshold in major clinical guidance and expert reviews[4][6].
- Some sources describe 200–300 ng/dL as a gray zone where symptoms matter a lot[8].
- Many clinicians aim for a treatment target in the middle of the normal range, roughly 450–600 ng/dL or 350–750 ng/dL, once therapy is started[6][1].
So the short answer is: less than 300 ng/dL is generally considered low enough to evaluate for treatment, but not everyone with a low number needs testosterone therapy[4][2][6].