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Short answer: a letter of medical necessity is a letter from a prescribing practitioner (or a supplier) that explains why an item is needed. For Medicare durable medical equipment (DME), the letter does not replace the standard written order or the medical record, and DME contractor guidance says attestation letters are not part of the medical record. A useful sample is therefore a structure that points to the record, not a block of clinical argument. This page is general information, not medical, legal or billing advice.
Who searches this: a clinic administrator, lab or supply manager, or practitioner’s office preparing paperwork for equipment or supplies. After reading, you should know what to put in a letter, what to attach to it, and what a letter cannot do by itself. Related reading: what a CMN is and how it differs from a written order, DME HCPCS code families and a worked coverage example for hospital beds.
Definition and scope
“Letter of medical necessity” (LMN) is a common name for a free-form letter, usually signed by a treating practitioner, that supports a request for an item or service. It is not a single federal form. This page covers the Medicare DME setting, where the documentation rules are published by CMS and the DME Medicare Administrative Contractors (MACs). Requirements for private insurers, employer plans and tax-advantaged accounts vary by payer and are not covered here.
One wording point matters. CMS Article A55426, “Standard Documentation Requirements for All Claims Submitted to DME MACs” (checked 2026-11-01), is revised from time to time. Its current text does not use the phrase “letters of medical necessity”; a 2024 revision (R20, effective 01/01/2024) replaced earlier language that named “attestation letters (e.g. letters of medical necessity)”. The article is labelled a draft article, and the applicable local coverage determination and related policy articles take precedence.
How a letter is used in practice under Medicare DME documentation
Three published statements frame what a letter can do:
- CMS Article A55426: “Supplier prepared statements and physician attestations by themselves do not provide sufficient documentation” of medical necessity, even if signed by the ordering physician. Records from suppliers or healthcare professionals with a financial interest in the claim outcome are not considered sufficient by themselves for determining that an item is reasonable and necessary.
- CMS Article A55426: templates and forms are subject to corroboration with information in the medical record, and the contemporaneous medical record is the source required to justify payment in a claim review.
- Noridian JD DME (a DME Medicare Administrative Contractor page, not CMS itself; page last updated 2024-09-26, checked 2026-11-01): “attestation letters (e.g. letters of medical necessity) are deemed not to be part of a medical record” for Medicare payment purposes, and the same applies to supplier-produced records signed by the prescribing practitioner.
In practice, a letter is a convenience that summarises and points to documentation. The documentation that carries the weight is the medical record and the written order.
Letter vs written order vs medical record
This comparison is the part most template pages skip. Each row below is based on the sources listed at the end of the page.
| Document | What the sources say | Source |
|---|---|---|
| Letter of medical necessity | Attestation letters are deemed not to be part of a medical record; a supplier-prepared statement or attestation is not sufficient by itself. | Noridian; CMS A55426 |
| Standard written order | Must include the beneficiary name or Medicare Beneficiary Identifier, a general description of the item, quantity if applicable, order date, treating practitioner name or NPI, and the treating practitioner’s signature. | 42 CFR 410.38(d)(1)(i) |
| Medical record | The source required to justify payment in a claim review; information on a prescription must be corroborated by it. It is not limited to the treating practitioner’s office records and may include hospital, nursing facility or home health records. | CMS A55426; Noridian |
| Face-to-face encounter documentation | Documented in the pertinent portion of the medical record. On request by CMS or its agents, a supplier must submit additional documentation to support and/or substantiate the medical necessity of the item. | 42 CFR 410.38(d)(3) |
For items on the Required Face-to-Face Encounter and Written Order Prior to Delivery List, 42 CFR 410.38(d)(1)(ii) requires the order to be communicated to the supplier before delivery; for other DMEPOS items the order is needed before the claim is filed.
Sample letter structure (placeholders only)
Because a letter cannot stand in for the record, a sample should be a skeleton. The outline below contains no clinical rationale. Whatever clinical statements a practitioner writes belong to that practitioner and must match the medical record.
| Section | Placeholder content |
|---|---|
| Header | [Practitioner letterhead] [Date] |
| Identifiers | [Beneficiary name or MBI] [Treating practitioner name and NPI] |
| Item | [General description of the item, quantity if applicable, worded the same as the written order] |
| Reference to record | [Dates and locations of the medical record entries and face-to-face encounter that support the order] |
| Practitioner statement | [Written by the treating practitioner from the record; not drafted by the supplier] |
| Signature | [Treating practitioner signature and date] |
Pre-send checklist
- The written order contains every element in 42 CFR 410.38(d)(1)(i), including the signature and order date.
- The item description in the letter matches the written order.
- The medical record entries the letter refers to exist and are dated.
- The letter is signed and dated by the treating practitioner.
- No claim in the letter goes beyond what the medical record contains.
Where it matters for labs, clinics and supply decisions
For clinics and suppliers handling DME, the practical consequence of the sources above is that review looks to the medical record and a complete written order. A letter prepared by a supplier carries less weight than the record, according to CMS. Staff can use the checklist above to confirm the supporting documents exist before relying on a letter. Coverage criteria are set per item in the applicable policy; see the hospital bed example and the guide to DME fraud schemes.
Common misunderstandings
“A signed letter proves medical necessity.”
Not by itself. CMS states that supplier-prepared statements and physician attestations alone are not sufficient documentation, even when signed by the ordering physician.
“The letter is part of the medical record.”
Noridian states that attestation letters are deemed not to be part of a medical record for Medicare payment purposes.
“There is one official form.”
None of the Medicare sources cited on this page names a single mandatory LMN form for Medicare DME. Certificates of medical necessity are a different, item-specific document; see the CMN guide.
FAQ
What is a sample letter of medical necessity?
A skeleton showing the sections a letter usually has: identifiers, the item, references to the medical record, the practitioner’s statement and a signature. The skeleton above uses placeholders only.
Are there letter of medical necessity examples I can copy?
Manufacturers and templates publish examples, but the clinical wording must come from the treating practitioner and match the record. CMS treats supplier-prepared statements as insufficient by themselves.
Is there a letter of medical necessity form?
An LMN is free-form. The Medicare documents with defined content are the standard written order (42 CFR 410.38(d)(1)(i)) and, for certain items, the CMN.
Does the IRS use the term?
IRS Publication 502 (2025, checked 2026-11-01) does not use the term “letter of medical necessity”. It does say that some expense types require a physician’s statement or recommendation, so check the publication for the specific expense.
Sources
- CMS Medicare Coverage Database, Article A55426, Standard Documentation Requirements for All Claims Submitted to DME MACs: cms.gov article A55426 (checked 2026-11-01).
- Noridian JD DME, Medical Records: med.noridianmedicare.com medical records (checked 2026-11-01).
- 42 CFR 410.38, Durable medical equipment, prosthetics, orthotics and supplies (DMEPOS): Scope and conditions: law.cornell.edu 42 CFR 410.38 (checked 2026-11-01).
- IRS Publication 502, Medical and Dental Expenses (2025): irs.gov Publication 502 (checked 2026-11-01).
