If a carrier denies your claim before payment, it is possible the only thing you will see is a standard remittance advice (RA). But you should go ahead and ask for more information.
In Transmittal 120, dated Aug. 25, the Centers for Medicare & Medicaid Services instructs the carriers to keep "more detailed information" in an accessible location so they can explain to you in more detail why they denied the claim.
For postpayment denials involving "complex review," the carriers should indicate whether they reviewed your documentation. And carriers should be careful choosing which category they place your denial in. Beneficiaries have different liabilities for statutory exclusion denials, benefit category denials or "reasonable and necessary" denials, CMS points out.