What is medical necessity?
A service is medically necessary when it's reasonable and needed to diagnose or treat the patient's condition, as defined by the payer's policy. Services that don't meet it are denied, usually as CO-50.
Medical necessity review
- Service
- 72148 MRI lumbar spine
- Payer policy
- Example Health Plan medical policy, section 4.2
| Policy criterion | Met? | Evidence |
|---|---|---|
| Six weeks of conservative care | Yes | PT notes, Nov 2 to Dec 18, pp. 4 to 9 |
| Neurological deficit on exam | Yes | Exam note, Jan 12, p. 2 |
| Imaging will change treatment | Yes | Surgical consult requested, Jan 14, p. 11 |
- This table is the core of both a prior authorization request and an appeal. Built once, it serves both.
Payers pay for care that is necessary for the patient’s condition, and they define necessary in their policies: Medicare’s LCDs and NCDs, and each commercial payer’s medical policies.
How it’s judged
The payer compares the claim, and sometimes the record, with its policy: the diagnosis, the patient’s history, prior treatment, test results and how often the service was given. If the documentation doesn’t show the criteria were met, the service is denied, most often as CO-50.
Where the answer lives
Medical necessity is proven in the clinical record, not the claim. The strongest appeals quote the payer’s policy and show, criterion by criterion, the note or result that meets it. The best prevention is checking the same criteria before the service, through prior authorization or a pre-service review, and documenting what the policy asks for.
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