"MG tests are all based on searching for the antibodies that work against enzymes that clean up excess Acetylcholine."

The tests are for AchR AB. The antibodies are against the acetylcholine receptors (not against acetylcholinesterase, the enzyme which breaks down acetylcholine).

So you need to have extra acetylcholine present a lot of the time so that it gets into the receptors whenever it can.

Mestinon (not antibodies) inhibit/s acetylcholinesterase, the enzyme which breaks down acetylcholine. A very good thing

(maybe just memorize the words, you can reconstruct what they mean when you say it out slowly).

"Is there no test for Acetylcholine itself.

It occurs to me that those who are seronegative, may simply have a naturally low level of Acetylcholine."

There is a form (maybe more than one) of CMS caused by insufficient release of acetylcholine from nerve terminals. That would be treatable with Mestinon, again, the idea being to save all available acetylcholine actually released from the usual breakdown (by normal levels of acetylcholinesterase.) Mestinon inhibits the breakdown enzyme, the acetylcholinesterase

I don't know how much anyone ever wants to test for a CMS so to the extent they don't, a patient could actually have insufficient acetylcholine release.