Oh my goodness! I just realized I forgot salivary cortisol levels in my previous posts about cortisol testing for Cushing's Disease!!!
Midnight Salivary cortisol levels are checked at...you guessed it...Midnight, and use a sample of (You guessed this one too, didn't you?) saliva. Yep, spit. This is another "Gold Standard" test used today by endocrinologists to diagnose Cushing's. It's a simple test you can do at home, freeze, and take with you to the lab when it's convenient to you. It is especially helpful for cyclic patients. You can wait till midnight (really, it is often done at 11pm) and if you don't feel high, you don't have to test and can save it for another night.
Because cortisol should be at its lowest at night, at nearly zero, and because Cushing's frequently causes high cortisol at night (flipped diurnal rhythm), it is a great time to test for abnormal highs Anything above 0.09 on a midnight salivary cortisol is diagnostic for Cushing's, assuming you didn't accidentally contaminate the sample (via bleeding gums, cosmetics, etc). Generally contaminated samples are sky high, though, or are marked by the lab as contaminated.
The collection containers may be little plastic tubes you spit into, but more often now they are little cotton swabs that fit inside those tubes. (Think of a mini-tampon, and you've got the right idea.) You don't eat or drink (or brush your teeth) for X amount of minutes before the test, and then you put it in your mouth and let it absorb as much saliva as you can. Then you place it in the tube, seal it, label it, place it in it's bag, and then in the freezer till the next day you go to the lab. I don't know how long these hold, so I wouldn't wait forever, but you can definitely go a few days. LabCorp seems to be using a newer collector model that to me looks like a mini lol.ipop with a plastic handle. Whatever the method, it's all quite similar.
*Note that there are a number of saliva testing labs online that do it via the mail...these results are generally not accepted by doctors, better to get a doctor to order the test and do it through a standardized lab if you want to use it for diagnostic purposes*