Yes, your test is inaccurate. They should have adjusted WHEN you took the dex (which should have been late at "night" for you and the blood should have been drawn "early in the morning" for you.
The result was a fail for most doctors - which sadly means your doctor is what I call an endodud - as the dex test is not the best test and while the docs tend to give it as they think it is super easy woohoo yeah I know so many that fail it - myself and hundreds others - that find out later that oh yeah... um, it was not a good indicator. If you really research the action of dex - it is a better test of location which means if you fail, it can mean more that the location is likely pituitary which is the most common source!
BTW the range means nothing for this test you want to just get above 1.4 if I remember correctly.
If your doc was decent, he would have run 24 hour urine testing - which is not dependent on your sleep schedule (it can be any 24 hours) and calculate the proper time to do what would be an 8am for you - my advice - find another doctor and when you give this test to another, write on it that this test was done after a night shift etc - a good doc will dismiss. If not, then you have another dud!
My doctor called me and said that what I'm talking about is a different test, that when I took it doesn't matter and that since my levels were suppressed with the dexamethasone, there is no indication of anything wrong. She is saying that I'm talking about looking for a deficiency when they were looking for a surplus. I'm so frustrated. Is there a difference between an "am cortisol test" and a "1 mg dexamethasone suppression" test? This test is supposed to measure if the levels are suppressed during my morning spike of cortisol, correct? So it would be the same as having someone take the pill and test them at 4 am while their cortisol levels are very low anyway? I'm trying to get my story straight to talk to my PCM to get a different referral.
With either test - you would have to do it at the correct time for your shift. I cannot see how it is accurate - and you need more than one test anyway.
The tests do differ but time is important to both. You need a referral - and the other doc needs to be smarter. I can find references but all say the midnight saliva tests are influenced by shift work - which is ok, but then why not 8am tests as well - so if one test is messed up by time, why not all?
For the endodud:
"The influence of gender, age, and coexisting medical conditions on the late-night salivary cortisol concentrations has not been fully characterized. It is important to note that the circadian rhythm is blunted in many patients with depressive illness and in shift workers (69,70) and may be absent in the critically ill (71). " http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2386281/
"Several studies have validated late-night salivary cortisol determination as a useful screening test for hypercortisolism (10, 23, 32, 33, 34). Cortisol in saliva is in equilibrium with free plasma cortisol, is independent of salivary flow rate, and stable at room or refrigerator temperatures. For these reasons, the measurement of cortisol in saliva has some advantages: it is easy to perform at home, and it is a noninvasive test. However, there are several conditions that can cause false-positive results such as poor diabetic control, obesity, depression, stress, shift work, and behavior (variable bedtime, licorice, cigarettes, and chewing tobacco). Following the recent recommendation of The Endocrine Society, two measurements of nighttime salivary cortisol are recommended to screen patients with suspected hypercortisolism despite some limitations. In fact, using various assays to measure cortisol in the saliva, a strict standardization of both collection and analysis methods is necessary, and normal reference ranges and diagnostic cutoff should be validated in each laboratory before being applied to a large population (35, 36). " http://jcem.endojournals.org/content/94/9/3121.full