Sorry am not Carol - not sure I understand the question correctly but cortef is hydrocortisone which is cortisol, so it can be measured accurately  in the blood. My son has cortisol and 17 OHP profiles done regularly. He has had many different tests to see how much he cortisol he absorbs from the oral hydrocortisone tablet, as well as IM and IV.  He has also had tests to see how quickly metabolises and clears it from the system. Pred and dex work differently and cortisol when using them cannot be accurately be measured as far as I understand.  I hope this helps.