Symptomatic men get dismissed for a simple reason: someone read one number without context. A proper read usually finds something treatable.
One number is not enough
Most of your testosterone is not available to your tissues. Roughly 60 to 65 percent is bound tightly to sex hormone binding globulin and is biologically inactive. Only 1 to 2 percent circulates completely free.
That is why a man can have a normal looking total testosterone and real symptoms. If his SHBG is high, more of that total is locked up. If his iodine is low, testosterone has a harder time getting into the cell where it works. If his LH is elevated, his hypothalamus and pituitary are shouting for more testosterone than his testicles are providing, and that is a diagnosis hiding in plain sight. Measuring only the total misses all of it.
Timing and age both matter
Testosterone peaks in the early morning, so an afternoon draw can look low in a man whose morning value is normal. A diagnosis rests on a morning draw, and it should be a full hormone panel, not testosterone alone.
There is no single agreed cutoff, more than eleven published guidelines exist, and medicine has never settled on good age-specific normals. The diagnosis cannot ride on one threshold. It has to come from the combination: the symptoms, the testosterone, and the numbers around it read together.
The reversible cause nobody wants to hear
A large share of low testosterone is functional, meaning something correctable turned the signal down. Obesity is the biggest driver, because fat tissue converts testosterone to estradiol, and estradiol suppresses the brain's signal more strongly than testosterone does.
Australian research in men reporting excellent health found testosterone did not fall with age at all. Once you account for body fat and general health, the age effect largely disappears between roughly seventeen and seventy.
Some men truly are low and need replacement. Others do not need replacing so much as optimizing. Sorting out which is which is half the work. Treating it well is the other half.
If you want children, say so first
Conventional testosterone therapy suppresses sperm production. Men who may want to father children should not start it until family building is finished. There are alternatives that raise your own production instead of replacing it. If nobody asked you about this, that is a red flag.