How does a medical necessity review work, and what slows it down?
A request arrives with clinical documentation. A reviewer, usually a nurse, reads the chart and tests it against the coverage criteria that apply: Medicare national and local coverage determinations, the plan's own policies, or a licensed guideline set. Medicare's statutory standard excludes services that "are not reasonable and necessary for the diagnosis or treatment of illness or injury." Requests that meet criteria are approved. The rest go to a physician.
Most of the time goes to finding facts. Lab values, imaging results, failed conservative treatment and dates of service sit in faxed notes and EHR exports, and each criteria branch needs a specific one. Two reviewers can read the same chart and land differently.
Errors are costly in both directions. An HHS Office of Inspector General review of Medicare Advantage denials from June 2019 estimated that 13 percent of denied prior authorization requests "met Medicare coverage rules," and found plans asking for documentation when the case file "was already sufficient to demonstrate medical necessity."