Saliva cortisol test - how accurate can a saliva test be?

Very accurate.: Saliva cortisol test is great for finding out if you are overproducing cortisol. Collected at midnight (assuming a normal sleep/awake pattern), salivary cortisol level is normally very low. When elevated, it indicates that a patient may be overproducing cortisol (cushing syndrome). The salivary cortisol test is not a good test for detecting underproduction of cortisol (adrenal insufficiency).

Check normal range: Accuracy of all tests is an issue and if the test does not reflect what appears clincally it may be need to be repeated. Accuracy depends on sensitivity and specificity. Trials need to be run comparing blood and saliva to determine which is best... And which is best for the money.