I realise that I may have wrongly assumed that the 400+ nmols/L (13,ooo+ ng/dL) was a baseline level of 17-OHP, or was it a post ACTH stimulation test level? Although regardless, I think, the fact that he is tanned still points to adrenal insufficiency.

Have you got a copy of your son’s other results, eg. cortisol, pre and post stimulation?