Those familiar with low T are aware of the two primary causes of low testosterone - Primary and Secondary Hypogonadism (either your brain or your testicles don't work) but there are also possible physiological reasons for low T that often go ignored:

Hydrocele - a hydrocele is a build up of water in the scrotal sack. The build up of fluid can cause pressure that can reduce blood flow and impair the normal functioning of the testes.

http://www.webmd.com/parenting/baby/tc/hydrocele-topic-overview

Variocele- a variocele is an enlargement of the blood vessels in the scrotum, the change or restriction in blood flow can inhibit the normal functioning of the testicles

http://www.mayoclinic.org/diseases-conditions/varicocele/basics/definiti...

I found these while researching TRT treatment protocols. I have seen two separate doctors for hormone level consultations and while they had differing of opinions of using testosterone, neither of them considered physiological reasons for Low T. I wonder how many people have Low T due to a condition that could be fixed with simple surgery? Nobody likes the doctor feeling on your junk but shouldn't a physical exam be incorporated into the diagnostic process? Guess that monthly check on your balls is worth a second look....