What does "not medically necessary" mean on an insurance denial?

The plan decided the service or drug does not meet its clinical criteria for your diagnosis or situation. That is a coverage decision based on the plan medical policy, not a statement that your clinician was wrong. You can appeal by showing how your records meet each criterion the plan cited on the denial letter or Explanation of Benefits.

How long do I have to appeal a medical necessity denial?

The deadline is printed on your denial notice or Explanation of Benefits. ERISA employer plans often allow up to 180 days for internal appeal, ACA marketplace plans commonly use shorter windows, and Medicare Advantage or Part B notices follow Medicare redetermination rules on Medicare.gov. Calendar the date the day you receive the notice and confirm the filing channel on that same document.

What documents prove medical necessity for an appeal?

A strong packet usually includes the denial letter with reason codes, a signed letter of medical necessity from your treating clinician, visit notes and test results, documentation of failed conservative treatment when the plan requires it, and excerpts from the plan policy or specialty guidelines your clinician cites. Number attachments so the reviewer can match each fact in your appeal to a record.

Can I appeal a medical necessity denial myself or does my doctor have to?

You file the appeal as the plan member through the portal, fax, or address on your notice. Healthcare.gov notes that you may include a letter from your doctor when you appeal a not medically necessary denial. A detailed clinician letter addressing the specific denial reason code carries more weight than a patient-written summary alone.

How do I find the clinical criteria my plan used?

Start with the denial letter or Explanation of Benefits. It often names a reason code such as CO-50 and a short rationale. Request the medical policy section cited on the notice from member services or your employer benefits office for ERISA plans. Map each bullet in that policy to a paragraph in your appeal and attach records that prove each point.

Is a medical necessity denial the same as an experimental or investigational denial?

No. A not medically necessary denial usually means the plan believes your records did not meet clinical criteria for a covered benefit. An experimental or investigational denial means the plan classifies the service as unproven or outside its covered benefit category. The appeal arguments differ. If your notice uses investigational language, read the plan policy for that separate pathway.

Can AppealFlow help me write a medical necessity appeal letter?

Yes. AppealFlow offers a free medical necessity appeal generator that drafts regulation-informed appeal language from your denial reason and facts. Pair the patient appeal letter with a signed letter of medical necessity from your treating clinician. Edit every line before you send it through the channel named on your notice.

Health Insurance Claim Denied as “Not Medically Necessary”: How to Fight Back

Q: What if my medical necessity appeal is denied internally?

An upheld internal decision is not always the last step. Healthcare.gov explains that many non-grandfathered plans must offer external review when you disagree with a medical necessity determination after internal appeal. Medicare uses its own appeal levels described on Medicare.gov. Keep copies of everything you already sent because external reviewers often work from the same record set.

By AppealFlow editorial•12 min read•Published July 2026•Updated September 2026

Flowchart of a not medically necessary insurance denial appeal showing denial letter review, clinical policy, letter of medical necessity, and internal appeal filing

When a health insurance claim is denied as not medically necessary, the plan decided your records did not meet its clinical criteria for the service or drug ordered. Request the denial letter and plan medical policy the same day, ask your treating clinician for a signed letter of medical necessity, and file the internal appeal through the channel named on your notice before that deadline passes. Healthcare.gov lists medical necessity denials as appealable, and Medicare.gov describes a separate redetermination path for Medicare notices.

What Does “Not Medically Necessary” Mean on a Denial?

Key Takeaway: The label means your submitted records did not satisfy the plan's clinical criteria, not that treatment is inappropriate in every setting. The reason code on your Explanation of Benefits tells you which criterion failed and what evidence to assemble.

Insurers apply medical policies that may require conservative treatment first, specific symptom patterns, or specialty society criteria before approving surgery, imaging, therapy, or specialty drugs. Common subcategories behind a not medically necessary denial include:

Conservative treatment not documented: The plan wants proof you tried physical therapy, medications, or rest before approving advanced imaging or surgery.
Clinical criteria not met: Your symptoms or test results do not match the plan's reading of specialty guidelines such as ACR, NCCN, or AAOS criteria.
Frequency or duration limits: You exceeded allowed visits, sessions, or units for the service type under the plan policy.
Wrong benefit category: The service may be covered under a different code or requires prior authorization that was never obtained.

Find the denial reason on your Explanation of Benefits. Look for remark codes, CARC/RARC codes such as CO-50, or a short clinical rationale. Cross-reference that language with the plan medical policy, usually available through member services or your employer benefits office for ERISA plans.

What Should You Do First When You Get This Denial?

Key Takeaway: Same-day actions matter more than a perfect letter draft. Confirm the appeal deadline, request the plan policy section cited on the notice, and start a numbered attachment list before you write a single paragraph.

Healthcare.gov's internal-appeals page states that you can appeal when a plan denies a claim because a service is not medically necessary. The page tells you to include your name, claim number, and member ID, and to send any information you want considered, such as a letter from your doctor.

For Medicare Advantage or Part B notices, Medicare.gov's appeals page describes redetermination and higher appeal levels with deadlines printed on the Medicare notice. Do not assume commercial plan clocks apply to Medicare.

Calendar the appeal deadline from your denial letter the day it arrives.
Request the complete claim file or medical policy section the plan used, if your plan type allows it.
Ask your treating clinician for a signed letter of medical necessity tied to each cited criterion.
Start a numbered attachment list: denial letter, appeal letter, clinician letter, visit notes, test results.

How Do You Appeal a Medical Necessity Denial Step by Step?

Key Takeaway: File the internal appeal before the deadline on your notice, attach a complete clinical packet with a detailed clinician letter, and request a written decision. Incomplete packets are a common reason reviewers uphold the original denial on first review.

Confirm your appeal deadline and filing channel. ERISA employer plans often allow up to 180 days for internal appeal. ACA marketplace plans commonly use shorter windows printed on the notice. Medicare uses separate clocks on the Medicare notice. See our guide on how long you have to appeal a health insurance denial for plan-type caveats.
Request documents the plan used. For many ERISA plans, you can request the claim file the reviewer relied on. Having that file helps your clinician address the exact gap the plan identified.
Get a letter of medical necessity from your treating clinician. It must address the specific denial reason code and cite accepted clinical guidelines by name. See our guide on how to write a letter of medical necessity for structure and prescriber attestation requirements.
Document failed conservative treatment when the plan requires it. Include physical therapy records, medication trials, rest periods, and specialist referrals with dates and measured outcomes.
Attach relevant diagnostic results. Imaging reports, lab values, pathology results, and visit notes showing symptom progression support the clinician letter.
Write and submit your formal appeal letter. Include member ID, claim number, date of service, provider NPI, and a numbered attachment index. Use the medical necessity appeal generator for a starting draft, then edit every line.
Submit through the correct channel and confirm receipt. Use the portal, fax, or mailing address on your denial letter. Save confirmation numbers and portal screenshots.
If denied again, request external review. An independent reviewer evaluates your case under rules described on external review in health insurance.

Weak vs Strong Appeal Wording

Key Takeaway: Medical directors approve appeals backed by clinical guidelines and objective data, not general frustration. Replace vague requests with dated metrics, guideline citations, and specific denial code references.

Weak wording	Strong wording
“My doctor ordered this MRI because I have back pain and nothing else has helped.”	“I appeal denial code CO-50 dated 08/12/2026 for CPT 72148. Attachment 2 is my neurologist's letter addressing plan criterion 3.b on conservative care failure. Attachment 3 lists six weeks of documented physical therapy with dates and measured outcomes.”
“This treatment is standard and my doctor recommends it.”	“Treating physician attests that conservative management per plan criteria Section 3.1 has been exhausted: NSAIDs for six weeks, two epidural injections with documented pain scores above plan thresholds. Surgery is indicated per AAOS clinical practice guidelines cited in Attachment 4.”
“Please reconsider. I really need this procedure.”	“I request internal appeal under the process named on my denial notice dated 08/01/2026. Attached: letter of medical necessity, physical therapy records, imaging report, and plan policy section 4.2.1 cited on the denial addressing each listed criterion.”

Need a Medical Necessity Appeal Letter?

AppealFlow builds a regulation-informed appeal from your denial reason and clinical facts. Edit live, then download PDF or Word.

Draft your medical necessity appeal letter

What Clinical Guidelines Should You Cite?

Key Takeaway: Name the guideline your plan policy references, cite the specific criterion your case meets, and attach the relevant page or excerpt. A generic statement that guidelines support treatment is weaker than naming the variant or recommendation level.

Effective medical necessity appeals reference specialty society criteria by name when they match the service type:

Imaging (MRI, CT, PET): American College of Radiology Appropriateness Criteria
Cancer treatment: National Comprehensive Cancer Network Clinical Practice Guidelines
Orthopedic surgery: American Academy of Orthopaedic Surgeons clinical practice guidelines
Physical therapy: APTA clinical practice guidelines for the relevant condition
Cardiology: ACC/AHA guideline documents for the relevant procedure or test

Your clinician's letter should quote the specific guideline variant that applies to your presentation. For imaging denials, see our guide on how to appeal a denied MRI scan for ACR citation examples.

How Do You Document Failed Conservative Treatment?

Key Takeaway: Most medical necessity denials require proof that less invasive options were tried first. Document each therapy with start and end dates, duration, outcome, and reason for discontinuation, not just a checkbox.

If your denial cites conservative treatment requirements, your appeal should document each therapy in this format:

Therapy type (physical therapy, NSAIDs, epidural injection, etc.)
Start and end dates that meet minimum duration in plan criteria, often four to eight weeks
Frequency and provider (for example, PT three times per week for eight weeks at a named clinic)
Outcome: pain scale change, functional improvement, or reason for discontinuation

Stating you tried physical therapy without visit notes or a discharge summary is usually not enough. Insurers want records from the treating provider documenting sessions attended and outcomes measured. For therapy denials specifically, see our physical therapy denial appeal guide.

What Deadlines Apply to Medical Necessity Appeals?

Key Takeaway: The controlling clock is on your denial notice, not a blog post. ERISA, ACA marketplace, and Medicare each use different internal appeal windows and external review rules.

Plan type	Typical internal appeal pattern	Where to verify
ERISA employer group health	Often up to 180 days from notice for internal appeal	Denial letter, Summary Plan Description, DOL EBSA materials
ACA marketplace / individual	Deadline printed on notice; external review after internal denial	Healthcare.gov internal and external review pages
Medicare Advantage / Part B	Redetermination and higher levels on Medicare notice	Medicare.gov appeals page and your Medicare notice

For a side-by-side comparison of internal appeal and external review, see internal appeal vs external review. Calling your insurer without filing a written appeal does not start the appeal clock or create the review rights named on your notice.

Check your notice before you write. A contractual exclusion is not the same as a medical necessity denial. If the plan says the benefit is not covered at all, the appeal path may differ from a clinical criteria dispute.

What If the Plan Upholds the Denial?

Key Takeaway: An upheld internal decision is not always the last step. Many non-grandfathered plans must offer external review when you disagree with a medical necessity determination after internal appeal.

Healthcare.gov's external-review page explains that you can ask an independent organization to review certain denials, including many medical necessity decisions, after the plan upholds an internal appeal. Medicare uses its own appeal levels on the Medicare notice.

If the plan denies your claim twice, read what to do when insurance denies a claim twice for next-step options. Keep copies of everything you already sent because external reviewers often work from the same record set.

Common Mistakes That Weaken Medical Necessity Appeals

Key Takeaway: The most common failure is submitting a patient-written letter without a detailed clinician letter addressing the specific denial code. Medical directors need clinical evidence tied to plan criteria.

Appealing without a clinician letter. Healthcare.gov notes you may include a doctor's letter, and that letter should address each criterion on the denial.
Not citing the specific denial code. Your appeal must respond to the exact reason on your Explanation of Benefits, not a generic request for coverage.
Missing conservative treatment documentation. If your plan requires therapy or medication trials first, prove you completed them with dated records.
Submitting to the wrong department. Prior authorization appeals and claim appeals follow different processes. Use the channel specified on your denial letter.
Stopping after internal denial. External review by an independent party may still be available under rules on your notice or Healthcare.gov.

Frequently Asked Questions

Denial meaning, deadlines, required documents, and how a patient appeal letter differs from a clinician letter of medical necessity.

Generate Your Medical Necessity Appeal Letter

AppealFlow.net drafts a regulation-informed appeal from your denial reason and facts. Pair it with your clinician's letter of medical necessity for a complete packet.

Medical Necessity Appeal Generator General Appeal Generator

100% Free
No Signup
PDF & Word Export

Disclaimer: This article is for educational purposes only and does not constitute medical, legal, or financial advice. AppealFlow.net is not a healthcare provider, insurance broker, or law firm. Appeal deadlines and medical policies vary by plan and program. Verify your denial notice, Healthcare.gov, CMS.gov, or Medicare.gov before you file. For medical emergencies, call 911. See our full disclaimer.