Hi L,
It is very important to know the 'units of measurement' - as you said! For instance if you live in USA your 17-ohp was likely to be measured in ng/dL and if you live in UK, Australia, Europe and just about everywhere else in the world 17-ohp is usually measured in nmol/L.
There is a big difference between ng/dL and nmol/L, so it cannot be assumed that because it appears low that it is. So for instance if 319 was nmol/L then this would be equivalent to about 10,600 ng/dL and likewise 1540 if in nmol/L would be very high.
There are two reasons why I think yours was probably measured in ng/dL:
1). You say that your testosterone was measured in ng/dL and this would be consistent also with the 17-ohp also being measured in Conventional Units.
2). I would think that had your levels been extremely high (as in 1540 nmol/L rather than ng/dL post acth test) then you would have had more extreme symptoms from an earlier age.
Providing there are no other factors which you are not aware of, I would be very concerned if your doctor wanted to give you "a horse dose to get the numbers down fast". Yes 1,540ng/dL (post-ACTH stimulation) is raised into the LOCAH range but not enough to have a large dose of steroid. Probably a small dose of Prednisone like M1 mentioned such as 2mg or 3mg initially would suffice, then retest after a couple of months to see what is happening to your Testosterone level.
If your doctor starts giving you "a horse dose" then I believe that the treatment will be worse than the condition itself. You will develop all sorts of side effects that you definitely do not need.
Keep us informed!