Only a very small amount of available cortisol is biologically active. A Genova Saliva Stress Test measures this available "active" cortisol (& DHEA) secreted at set times over a 24 hours period. The results will allow you to see any imbalances in the daily circadian pattern so enabling use of correcting supplements to aid your adrenal health. Unfortunately this test is not generally used or recognised by GP's.
Doctors usually conduct a 9am blood test which gives a snap shot of the available bound & unbound cortisol & is used more to assess the ability of the adrenals to produce adequate amounts of cortisol.
To measure free cortisol, urine may be collected over 24 hours, in a test called Urinary Free Cortisol (UFC), which measures excretion of the circulating, biologically active, free cortisol, as too much excretion may be a marker for adrenal dysfunction.. (Cushings ? ? ..)...
You cannot get accurate saliva results while on any kind of medication or supplement that will affect cortisol.
Saliva Stress Test (test ref END01)