Here is what they said in the study I mentioned earlier:
Results: In a reference sample of 456 men, mean (SD), median (quartile), and 2.5th percentile values
were 723.8 (221.1), 698.7 (296.5), and 348.3 ng/dl for TT and 141. 8 (45.0), 134.0 (60.0), and 70.0
pg/ml for FT, respectively. In all three samples, men with low TT and FT were more likely to have
slow walking speed, difficulty climbing stairs, or frailty and diabetes than those with normal levels.
(TT and FT = Total and Free Testosterone)
They also say that, for the purposes of the study, total T levels below the 2.5th percentile (i.e. about 350 ng/dl) were deemed to be low (meaning: they're the people with slow walking speed, difficulty climbing stairs, frailty and diabetes, with the implication that people with T levels that low should be placed on some kind of HRT).
Looking at these comments, it would appear that some doctors are telling their patients with total T below 350 ng/dl that it falls in the "normal" range. IMO it's not normal if your T levels put you in the bottom 2.5 percent of the population, and at high risk of experiencing health problems as a result.
Another important point that tends to be overlooked is the fact that that free T, not total T, is the important thing as far as biological effects are concerned, and SHBG (sex hormone binding globulin) has a large influence on free T levels. Unfortunately, free T is much more difficult to measure than total T so most laboratories only measure total T, and that's often the only measurement we're given, and the one doctors tend to look at. Nonetheless, free T, not total T, is the important thing as far as your body is concerned. If, like me, you have elevated SHBG levels, the SHBG ties up almost all the T in your system and you can end up with very little free testosterone, even if your figure for total T doesn't look too bad.
Unfortunately they didn't publish the SHBG measurements in that study, but in the hypogonadism forums I belong to, the consensus seems to be that the ideal level for SHBG in males is around 20 nmol/l. In the blood work I've had done, I've averaged about 40, which is no doubt a contributing factor to my developing symptoms of low T.