I don't think the testosterone assay has much value at all. Now that I have your collective attention, please allow me to explain why. In the first place, the "range" is lab specific, so you cannot compare the results from one lab with another, or even establish "standard" ranges. Some labs go for 300-1000ng/dL. Others drop as low as 240, others as high as 1750. Also, at a recent Hormone Replacement Therapy (HRT) conference I attended, one of the lecturers said they measured serum T levels of 150-1350ng/dL IN THE SAME PATIENT, ON THE SAME DAY!
Also, we are supposed to measure it in the morning, when it is highest. Well, what time of the day do we need our testosterone the most? Most are getting the kids off to school, running around getting ready, she's got her own thing going on...IOW, most people don't get the chance for romance until bedtime (when T is the lowest). And who needs that drop-out we feel around 4PM? Every successful man will tell you it is what he does AFTER 4PM that got him that way (again, when his T is lower than in the morning, when we are supposed to be testing it).
Besides, it is only the most severe cases of hypogonadism that T actually drops below "normal" (how I hate that word!). I regularly see guys who are experiencing all the symptoms of hypogonadism, yet their T comes back at 500 or over. So what am I supposed to do? Ignore his very real symptoms? How could I consider myself a compassionate doctor if I did??!! So I do "therapeutic testing": I jack him up on testosterone (to the upper quartile) and now his life is completely changed. Kinda' proves it, doesn't it?
Of course, it frequently goes the other way, too. A patient came to me complaining of very severe symptoms. Really, really miserable. I felt very bad for him, especially since he is such a good guy. Well, his labs came back at a whopping 91ng/dL. Actually, at that point, I think we were both quite relieved--we'd nailed it for sure. Now he is rockin'.
I would say that low T on a lab test has value because it's necessary for the insurance companies to pay for the Upjohn, but, so far, they have just accepted my ICD-9 Codes for hypogonadism, fatigue, and malaise (I usually do not include the one for Erectile Dysfunction--it is such a given).
At this point, the real value of the Total Testosterone is mostly to make sure I have not raised it too far. Besides the legal considerations of doing that (because I would then be prescribing steroids), it tends to shoot the Lipid Profile (but every single component of which improves until we pass the top of "normal" range). Also, going that high tends to exact a wear-and-tear on men after a while. Several times now my guys have told me they felt better once I had dropped them back down into the upper quartile.
So, we have to draw this assay, but must remain mindful we are treating real patients, not numbers on a laboratory printout.