@bdm105 Honestly, I'm not sure how they can discern whether this is diagnostic or not other than you being under the care of a doctor. I can see this being a problem if you go online and pay a high price for a test, then ask for reimbursement.
So basically, you can go online and grab a test for $200, but your insurance will likely push back if you submit for reimbursement. They have a schedule of payment and will only reimburse up to a point.
Your insurance will not completely reimburse you if you pay a marked up price for the test. The good news is that if you have a high deductible health plan, you do NOT have to pay for the test kit via your deductible.
Hearing tests that you buy for traveling. For example, you need to produce a negative test to fly into or out of the country / state depending on local situations are not covered by insurance either.