It is not your doctor's opinion versus theirs. It is a criteria document nobody shows you — and you have the right to see it.
Medical necessity is not a medical concept. It is a contract term. Every health insurance plan defines it in the plan documents, and that definition is what controls whether your care gets approved — not your doctor's clinical judgment.
Most plans define medically necessary care as: services that are appropriate and consistent with the diagnosis, not experimental or investigational, not more costly than an alternative service that would produce equivalent results, and provided in the most appropriate and least intensive setting.
Notice what is not in that definition: what your doctor thinks is best for you specifically. The definition is designed to give the insurer flexibility to apply criteria that serve their cost goals while sounding clinical.
Behind every medical necessity determination is a clinical criteria document. Insurers and utilization management companies like EviCore and Carelon publish guidelines that define exactly what conditions must be met for a service to be approved. These documents run to hundreds of pages and are updated regularly.
Your doctor is not given these documents. There is no requirement that a provider know the specific insurer criteria before submitting a prior authorization. Providers are expected to document medical necessity, but they are doing it without knowing exactly what the reviewer is checking against.
Medical necessity is the most useful denial language for an insurer because it is flexible. Almost any service can be denied on medical necessity grounds by applying the right criteria document with the right interpretation. It is harder to challenge than a flat coverage exclusion — because it puts the burden on you to prove the care was necessary rather than on the insurer to prove it was excluded.
It also sounds more legitimate. A denial that says "your plan does not cover this" is clearly a coverage decision. A denial that says "this was not medically necessary" sounds like a clinical finding. It is not. It is an administrative determination made by applying a written criteria checklist, often by a nurse or algorithm, and only sometimes reviewed by a physician.
When you receive a not medically necessary denial, the most important questions are:
The denial letter is required to give you the first two. Your doctor needs to address the third in any appeal. A good appeal does not argue generally that the care was needed. It directly addresses the specific criterion the insurer said was missing and provides documentation that satisfies it.
