How to fax a letter of medical necessity to an insurance company

Fax a letter of medical necessity, the clinician's statement that a service, device or drug meets the plan's own criteria, with the plan's prior authorization or appeal form to the number that form prints. The plan's clock runs from receipt: prior authorization decisions are due within 72 hours if urgent and 7 to 15 days if not.

What is a letter of medical necessity, and when does an insurer ask for one?

A letter of medical necessity is a clinician's written statement that a service, supply or drug is needed to diagnose or treat a condition and meets the plan's own coverage criteria, and an insurer asks for one when its own policy, form or guide says so. HealthCare.gov's definition of medically necessary covers health care services or supplies needed to diagnose or treat an illness, injury, condition, disease or its symptoms that meet accepted standards of medicine.

Four plan documents show when an insurer asks:

• Aetna Clinical Policy Bulletin 0434 (Therapeutic Chairs) asks for a letter of medical necessity when equipment is billed under an unlisted code.
• Cigna Medical Coverage Policy 0156 (TMJ disorder surgery, effective 12/15/2025) requires a letter for all TMJ surgery requests.
• Humana's CarePlus Health Plans quick reference prior authorization guide (08/25) asks for one for brand-specific durable medical equipment.
• Texas Department of Insurance form NOFR001, hosted on UnitedHealthcare's provider site, asks for a brief narrative of medical necessity in its clinical documentation section or in an attached statement.

What should a letter of medical necessity include?

A letter of medical necessity should carry the clinical facts the plan's own documents list: the diagnosis and history, the functional limitations, the treatments tried and why the requested item or service is needed. Each source names its own items:

• The Medicare Program Integrity Manual, Chapter 5, section 5.9 (DMEPOS items, meaning durable medical equipment, prosthetics, orthotics and supplies), says the patient's medical record should include the diagnosis and other pertinent information such as the duration of the condition, clinical course (worsening or improvement), prognosis, nature and extent of functional limitations, other therapeutic interventions and results, and past experience with related items.
• Aetna's bulletin asks, for an unlisted code, for the features of the equipment not available with standard equipment and accessories, and for the member's functional limitations and underlying medical condition that require those features.
• Cigna's policy asks for a detailed history of the condition, diagnostic imaging results and documentation of prior medical and surgical treatment.
• Humana's guide asks why the items covered under the Evidence of Coverage cannot meet the member's needs.

The same Medicare manual section says a physician's order, a certificate of medical necessity, a supplier-prepared statement or a physician attestation does not by itself provide sufficient documentation of medical necessity, even when the treating physician or supplier signs it. A letter for a Medicare equipment claim therefore needs the patient's medical record behind it.

Where do you fax a letter of medical necessity: prior authorization, appeal or exception?

A letter of medical necessity goes to the plan with the request it supports: with the plan's prior authorization form to the number that form prints, with an appeal to the plan's appeal line, and with an exception request to the plan's exception line. The table shows, for each kind of request, who receives the letter and the rule or deadline attached.

For a prior authorization, the plan's own form fixes the destination. Aetna's Orthognathic Surgery Precertification Information Request Form (GR-69324, 6-22) says its FaxHub number is for clinical information only and asks for specific information that supports the medical necessity review. How to fax a prior authorization or appeal and prove delivery covers what else goes in the fax, what stays off the cover sheet and how to prove receipt.

For an appeal, HealthCare.gov's internal appeals page tells people to submit any additional information they want the insurer to consider, such as a letter from the doctor. 29 CFR 2560.503-1 gives ERISA claimants the opportunity to submit written comments, documents, records and other information relating to the claim. The paths after a denial are in what to do when a prior authorization is denied.

For an external review, HealthCare.gov's external review page says plans that use the HHS-administered Federal External Review Process take the request by fax: call 1-888-866-6205 for the request form, then fax the request to 1-888-866-6190.

How long does the insurance company have to decide?

An insurance company's decision clock runs from the day it receives the request, and the program sets the length: 72 hours for an urgent request, 7 calendar days for a standard prior authorization at Medicare Advantage, Medicaid and CHIP payers under CMS-0057-F, 14 calendar days for some Medicare Advantage services and 15 days for an ERISA plan's pre-service claim.

The CMS-0057-F fact sheet says impacted payers must send prior authorization decisions within 72 hours for expedited requests and 7 calendar days for standard requests. Impacted payers are Medicare Advantage organizations, state Medicaid and CHIP fee-for-service programs, Medicaid managed care plans, CHIP managed care entities and Qualified Health Plan issuers on the Federally Facilitated Exchanges, and the exchange issuers are excluded from the two timeframes. The operational policies have a compliance date starting January 1, 2026.

Under 29 CFR 2560.503-1(f)(2), a group health plan decides an urgent care claim as soon as possible and no later than 72 hours after receipt, unless the claimant fails to provide sufficient information. A pre-service claim is due within a reasonable period and no later than 15 days, and the plan may extend that once by up to 15 days.

A Medicare Advantage organization has 14 calendar days for a standard determination on a service or item outside the prior authorization rules of 42 CFR 422.122, and from January 1, 2026, 7 calendar days for one inside them (42 CFR 422.568). An expedited determination is due as expeditiously as the enrollee's health condition requires and no later than 72 hours after the request (42 CFR 422.572).

Appeal windows run separately. ERISA plans give at least 180 days after notice of an adverse benefit determination to appeal, and an urgent appeal is decided no later than 72 hours after the request for review. HealthCare.gov says an internal appeal must be completed within 30 days for a service not yet received and 60 days for one already received. An external review request must be filed in writing within 4 months of the denial notice, and the decision is due within 45 days for a standard review and 72 hours for an expedited one.

How do you prove the insurer received the letter?

The proof that an insurer received a faxed letter of medical necessity is the sender's delivery record, which shows when the fax reached the plan's number. Every decision clock runs from the plan's receipt of the request, so that record dates the start. The ERISA rule counts from receipt of the claim by the plan, and the Medicare Advantage rule counts from receiving the request. The record belongs in the file beside the plan's reference number and the date of its reply.

CMS-0057-F lets the reply arrive by a different route than the request. From 2026, impacted payers must give a specific reason for a denied prior authorization decision, and decisions may be communicated by portal, fax, email, mail or phone.

What gets a letter of medical necessity rejected?

A letter of medical necessity falls short when it goes to the wrong recipient, leaves out an item the plan's own policy lists, stands alone without the medical record, or misses a window.

• A request sent to the wrong place: the Texas form NOFR001 instructions name the Texas Department of Insurance, the Texas Health and Human Services Commission and the patient's or subscriber's employer as places it does not go.
• A letter missing an item the policy lists: Cigna's TMJ surgery policy names a detailed history, diagnostic imaging results and documentation of prior treatment, and Aetna's bulletin names the equipment features and the functional limitations.
• A letter sent alone: under the Medicare manual, an order, a certificate of medical necessity, a supplier-prepared statement or an attestation is not sufficient documentation by itself.
• A clinical line used for other documents: Aetna's FaxHub number is for clinical information only.
• A missed window: an ERISA plan must give at least 180 days to appeal, and an external review request is due within 4 months of the denial notice.

The urgent path depends on the physician's statement. A Medicare Advantage organization must expedite a request made or supported by a physician when the physician indicates that the standard timeframe could seriously jeopardize the enrollee's life, health or ability to regain maximum function (42 CFR 422.570). Under 45 CFR 147.136, the attending provider determines whether a claim involves urgent care, and the plan or issuer defers to that determination. How to request an expedited prior authorization walks through marking the fax.

How does the same letter work for Medicare, Medicaid, Part D and FSA or HSA claims?

A letter of medical necessity works across Medicare, Medicaid, Part D and FSA or HSA claims when its clinical content meets each program's own test, and the tests differ.

• Medicaid decides medical necessity for a child eligible for Early and Periodic Screening, Diagnostic, and Treatment (EPSDT) case by case, taking into account the child's particular needs, according to the May 2026 Medicaid.gov EPSDT coverage guide.
• A Part D formulary exception takes the prescriber's supporting statement and its own clock, which how to fax a formulary exception with a letter of medical necessity covers.
• A Medicare durable medical equipment (DME) order rests on the medical record behind it, and Chapter 5, section 5.9 of the Medicare Program Integrity Manual lists what that record shows.
• An FSA or HSA claim follows IRS rules: IRS Publication 502 (2025) counts health institute fees as a medical expense only if a physician prescribes the treatment and issues a statement that it is necessary to alleviate a physical or mental disability or illness of the person receiving it.

How do you send letters of medical necessity from a HIPAA fax account?

A Fax Pigeon account sends the letter, the plan's form and the supporting records from the browser or from email, and a PDF, a Word file or a phone photo uploads as it is. The cover sheet is optional, which lets the plan's form open the fax. Every delivered fax gets delivery proof to file with the plan's reference number, and replies to the practice's own number land in a shared inbox where each can be assigned to a person on the team. Every plan includes a signed BAA at signup and unlimited people.

* Official sources (HealthCare.gov, eCFR, Centers for Medicare & Medicaid Services, Medicaid.gov, Internal Revenue Service, Aetna, Cigna Healthcare, UnitedHealthcare, Humana) were read on October 23, 2026. Fax Pigeon prices and plan terms as of October 24, 2026.