Demand the internal criteria
Request the specific clinical guideline, medical policy, coverage bulletin, or peer-review rationale used to deny the claim. A strong appeal answers the exact rule the plan relied on instead of arguing in general terms.
Medical Necessity Denial Guide
How to appeal a "not medically necessary" insurance denial
A notice saying treatment was not medically necessary is not the end of the claim. It is an administrative decision that can be challenged with the insurer's own criteria, your treating doctor's clinical rationale, and a complete evidence packet.
Strict Diagnostic Imaging Scope
IMPORTANT: This guide covers medical necessity denials (CO-50) for high-tech diagnostic imaging services, such as MRIs, CT scans, and PET scans, under CPT codes 70010 through 79999. Other medical necessity denials, such as oncology drug disputes or inpatient stay reviews, follow different processes and are not covered here.
Carrier Tactic
What the denial is usually doing
Insurers routinely use automated utilization software to compare your chart against rigid, algorithmic benchmarks (like Milliman Care Guidelines or InterQual) without accounting for your treating physician's clinical assessment or specific patient comorbidities.
Defense Strategy
How to challenge a medical necessity rejection
The appeal should turn a vague denial into a criteria-by-criteria clinical response supported by records and physician rationale.
Establish treating physician rationale
The appeal should show why the treating provider's direct clinical assessment is more complete than a paper review. Objective findings such as labs, imaging, active symptoms, failed therapies, and comorbidities are what turn the doctor's opinion into usable evidence.
Cite recognized clinical support
When appropriate, the appeal should reference professional society guidance, peer-reviewed literature, FDA-approved indications, or accepted standards of care. This forces the reviewer to address clinical evidence rather than rely only on internal policy language.
Appeal Workflow
How the dispute process works
To challenge this denial, specific administrative actions must be completed. Work through the steps in order.
Step 1: Request the Insurer's Clinical Policy
Triage SequenceWhat to do
You must locate the clinical policy bulletin, medical coverage guideline, or utilization review criteria cited in the denial letter. If it was not included, you must manually request it from the appeals department or search through your carrier's member portal.
Step 2: Obtain the Treating Doctor's Rationale
Triage SequenceWhat to do
You must ask your treating physician for a signed letter of medical necessity that addresses your specific condition, explains why the denied treatment was recommended, and outlines why lower-level or alternative therapies were not clinically appropriate.
Step 3: Assemble the Evidence File
Triage SequenceWhat to do
You must manually gather diagnostic reports, office notes, prior treatment history, medication records, therapy notes, lab results, imaging, and any recognized clinical guidance that supports the requested service from multiple clinics.
Step 4: Submit a Structured Appeal Packet
Triage SequenceWhat to do
You must physically combine your appeal letter, denial notice, clinical rationale, supporting records, signed HIPAA authorizations, and carrier-specific representative forms into one complete packet and mail or fax it through a trackable appeal channel.
Appeal Notes
What strengthens the packet
- A medical necessity appeal should identify the exact rule the insurer used and then match the patient's records against that rule.
- A short doctor note saying the treatment is necessary is usually weaker than a letter that explains symptoms, failed alternatives, objective findings, and risks of delay.
- If the denial was issued by a utilization review vendor, include the vendor tracking number and any clinical criteria referenced in the decision.
- Medical necessity is actually one of the least common reasons for in-network marketplace denials: only 5% in 2024, versus 36% for unspecified "other" reasons and 25% for administrative issues (KFF analysis of CMS data, published March 2026). A denial coded as medical necessity is worth double-checking against the plan's own clinical policy rather than assumed to be unbeatable.
Next Step
Have a medical necessity denial?
Answer a few questions about your denial and get an editable appeal letter you can review and send yourself.
Create Free Appeal LetterThis guide provides general administrative information for health insurance appeals. It is not legal or medical advice, and plan rules, appeal rights, and medical-necessity standards can vary.