Will taking Cortisol supplement affect Adrenal Saliva Test

Hi Guys,
I am on 20 mg Cortisol daily. I want to get a adrenal saliva test done because I feel that my cotisol dosage needs to be changed. Does anyone know if taking cortisol while doing the saliva test affect the test results. I take the whole 20 mg at morning. If I need to stop taking the Cortisol, then how many days should I wait before I can get accurate saliva test. I tried weaning off once in the past but had little success.

Regards
Suvro