What is a Letter of Medical Necessity and why do I need one?

A Letter of Medical Necessity (LMN) is a document from your doctor explaining why a specific treatment or device — like a CGM — is clinically required for your care. It is the single most important document in a CGM insurance appeal. It should reference your diagnosis, A1C history, hypoglycemic episodes, and alignment with ADA clinical guidelines.

What is an external independent review and how do I request one?

An external independent review is a review of your insurance denial by an organization that is completely independent from your insurance company. Under the Affordable Care Act, you have the right to request this review if your internal appeal is denied. Contact your state's Department of Insurance or look for the external review process instructions on your denial letter. The insurer must abide by the reviewer's decision.

Can I get CGM supplies without insurance while my appeal is being processed?

Yes. While your insurance appeal is pending, you can purchase CGM sensors and diabetes supplies out of pocket using your FSA or HSA account, which offers a tax advantage. MDS Diabetes (mdsdiabetes.com) carries FSA/HSA eligible CGM supplies with no prior authorization required, so you can stay protected while your insurance dispute is resolved.

How to Appeal a CGM Insurance Denial Step by Step

You Just Got Denied — Here's What to Do Next

Getting an insurance denial for your CGM sensors or diabetes supplies is frustrating, frightening, and frankly exhausting — especially when you depend on this technology to stay safe every single day. But here's the truth: a denial is not the end of the road. Insurance companies deny claims expecting many patients to give up. Don't be one of them. The appeals process exists specifically for situations like yours, and with the right steps, many denials get overturned.

This guide gives you exact steps, exact language, and exact deadlines to fight back — starting today.

Step 1: Get the Denial in Writing (Within 24 Hours)

If you received a verbal denial, immediately call member services and request a written Explanation of Benefits (EOB) or formal denial letter. This document must include:

The specific reason for denial (e.g., "not medically necessary," "non-formulary," "prior authorization not obtained," "step therapy requirements not met")
The clinical criteria used to make the decision
Your appeal rights and deadlines
The appeals process and contact information

Under the Affordable Care Act, insurers are legally required to provide this information. If they refuse, file a complaint immediately with your state insurance commissioner.

Step 2: Understand Why You Were Denied

The denial reason dictates your appeal strategy. Common CGM denial reasons include:

"Not medically necessary" — Most common. Your doctor needs to provide clinical documentation.
"Prior authorization not obtained" — Your prescriber may not have submitted the PA form, or it was incomplete.
"Non-formulary device" — The specific CGM brand isn't on your plan's approved list.
"Step therapy requirements not met" — The insurer wants proof you tried a cheaper alternative first.
"Experimental or investigational" — Outdated language still used against CGMs despite ADA guidelines supporting them.

Step 3: Call Your Insurer and Get the Internal Appeal Process

Call the member services number on your insurance card. Use this exact script:

"Hello, I'm calling about claim denial [reference number from your EOB]. I want to file a formal internal appeal. Can you tell me the exact deadline for filing, the address where I should send my appeal, and what documentation is required? I also need the name of the medical director who made this determination."

Critical deadlines: Most plans allow 180 days from the denial date to file an internal appeal. For urgent/expedited appeals (when your health is at immediate risk), the insurer must respond within 72 hours. For standard appeals, they have 30–60 days.

Step 4: Build Your Appeal Package

A strong appeal includes the following documents:

A written appeal letter (see sample below)
A Letter of Medical Necessity (LMN) from your endocrinologist or primary care physician — this is the most important document
Clinical records showing your diagnosis (Type 1 or Type 2 diabetes), A1C history, hypoglycemic episodes, or hypoglycemia unawareness
ADA Clinical Practice Guidelines citing CGM as standard of care (Standards of Medical Care in Diabetes, current year)
Published peer-reviewed studies supporting CGM efficacy
Your pharmacy or supplier records showing prescription history

Sample Appeal Letter

[Your Name] | [Address] | [Date]
[Insurance Company Name]
Attn: Appeals Department
[Insurance Company Address]

Re: Formal Appeal of Denial — Member ID [XXXXXXX] — Claim [XXXXXXX]

Dear Appeals Review Board,

I am writing to formally appeal the denial of coverage for my continuous glucose monitor (CGM) as issued on [denial date]. This device is medically necessary for the management of my [Type 1/Type 2] diabetes diagnosed on [date].

My physician, [Doctor's Name, MD], has determined that CGM technology is essential to my care because [brief clinical reason — e.g., "I experience hypoglycemia unawareness and have had multiple dangerous low episodes requiring emergency intervention"]. This is consistent with the American Diabetes Association's Standards of Medical Care, which explicitly recommends CGM use for patients with my clinical profile.

The denial citing "not medically necessary" is inconsistent with established clinical evidence. Enclosed please find my physician's Letter of Medical Necessity, my clinical records, and supporting ADA guidelines.

I request an immediate reversal of this denial. If this internal appeal is unsuccessful, I will pursue an external independent review through [your state] Insurance Commissioner and/or CMS, as is my right under the ACA.

Sincerely,
[Your Name]
[Phone Number] | [Email]

Step 5: If Internal Appeal Fails — Escalate Immediately

If your internal appeal is denied, you have additional rights:

External Independent Review: Under the ACA, you can request a review by an independent organization not affiliated with your insurer. They must respond within 45 days (or 72 hours for urgent cases). Insurers must comply with the external reviewer's decision.
State Insurance Commissioner: File a complaint at your state's Department of Insurance website. Many states have dedicated consumer assistance programs for exactly this situation.
Medicare patients: Contact CMS directly at 1-800-MEDICARE or submit a redetermination request through your Medicare Administrative Contractor (MAC).
Contact the ADA Advocacy Team: The American Diabetes Association offers free assistance navigating insurance denials at 1-800-DIABETES.

While You're Fighting — Don't Go Without Supplies

Insurance battles can take weeks or months. You shouldn't have to go without your CGM sensors or diabetes supplies during that time. MDS Diabetes (mdsdiabetes.com) carries a full range of CGM supplies, glucose monitors, test strips, and diabetes essentials — all FSA/HSA eligible with no prior authorization required. Order online today and ship directly to your door while your appeal is in progress. Your health can't wait for bureaucracy.

Key Takeaways

Always get your denial in writing with a specific reason
File your internal appeal within 180 days — sooner for urgent situations
A strong Letter of Medical Necessity is your most powerful tool
You have the right to an external independent review if internal appeal fails
Never stop advocating — many denials are overturned on first appeal

Frequently asked questions

Most health insurance plans allow 180 days from the date of denial to file an internal appeal. For urgent or expedited appeals where your health is at immediate risk, you can request a response within 72 hours. Always check your specific denial letter for plan-specific deadlines, as they can vary.

Editorial note

This article is for educational purposes only and does not constitute medical advice. Always consult your healthcare provider before making changes to your diabetes management. Last reviewed: July 27, 2026 by the MDS Diabetes editorial team.

What to do next

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How to Appeal a CGM Insurance Denial — Step by Step