Letters of Medical Necessity: What They Should Say and How to Ask for One

When insurance covers durable medical equipment, the decision often comes down to a single document: a letter from the prescribing provider explaining why the equipment is needed. This document is called a letter of medical necessity, and it determines more outcomes than most people realize. A strong one unlocks coverage. A weak one — or a missing one — leads to denials, appeals, and out-of-pocket costs.

This article walks through what a letter of medical necessity is, what it should contain, how to ask a provider for one, and what to do when the first letter isn't strong enough.

What a letter of medical necessity actually is

A letter of medical necessity (often abbreviated LMN) is a written statement from a licensed healthcare provider — typically a physician, but sometimes a nurse practitioner, physician assistant, or specialist — explaining why a specific piece of equipment, service, or treatment is medically necessary for a specific patient.

It is not the same as a prescription. A prescription tells the supplier what to provide. A letter of medical necessity tells the insurance reviewer why it should be paid for. Both are usually needed for higher-cost items, and they serve different functions in the approval chain.

Insurance reviewers — whether at Medicare, Medicaid, a private insurer, or a Medicare Advantage plan — generally don't know the patient. They review claims using documentation submitted by the prescribing provider and the equipment supplier. The letter of medical necessity is the document that translates a clinical situation into the language an insurance reviewer can act on. When it's specific, well-supported, and tied directly to the equipment being requested, claims get approved. When it's vague, generic, or doesn't clearly link the medical situation to the equipment, claims get denied.

When you need one

Not every piece of equipment requires a letter of medical necessity. Basic items prescribed through standard channels — a walker, a standard wheelchair, a basic shower chair — usually move forward on the prescription alone. Where letters become essential is for equipment that is:

Higher in cost. Power wheelchairs, complex rehab seating, specialized hospital beds, oxygen equipment, communication devices, and similar items typically require letters because the dollar amounts trigger more scrutiny.

Custom-configured or non-standard. Equipment that doesn't fit a basic catalog category — a wheelchair with specific seating components, a walker with custom features, a hospital bed with a specialty mattress — needs justification beyond a generic prescription.

Likely to be denied as "convenience" rather than necessity. Seat elevators on power wheelchairs, certain cushion upgrades, specialized controls, and similar items often get denied as not medically necessary. A strong letter that explains the specific functional purpose of the upgrade is what changes that outcome.

Replacement equipment within the standard useful lifetime. Medicare's default position is that a wheelchair should last five years and a hospital bed similar. If you need replacement earlier, you need a letter explaining why.

Subject to prior authorization. Many insurance plans, especially Medicare Advantage plans, require prior authorization for higher-cost equipment. The letter of medical necessity is part of that submission.

If you're not sure whether your equipment requires a letter, ask the prescribing provider or the equipment supplier. Both should know.

What a strong letter contains

A useful letter of medical necessity has six components, and missing any of them weakens the letter:

1. The patient's specific diagnosis or condition. Not just a category ("mobility impairment") but the actual diagnosis, with ICD-10 codes if possible. "Multiple sclerosis with progressive lower-extremity weakness" reads very differently to a reviewer than "trouble walking."

2. The functional limitations the condition causes. What can the patient not do that they need to do? "Unable to ambulate more than 10 feet without rest" or "unable to transfer from bed to chair without two-person assistance" or "unable to maintain seated posture without specialized support due to truncal weakness." Functional language matters because it ties the medical situation directly to what the equipment will address.

3. The specific equipment being requested. Not "a wheelchair" but "a Group 3 power wheelchair with tilt-in-space seating, full electronic positioning, and a custom-molded back support." The more specific the equipment description, the more the letter ties to the actual claim being submitted.

4. The medical reason this specific equipment is needed. Why this configuration, not a standard one? A reviewer needs to see the link: this patient has this condition, which causes this limitation, which requires this equipment, which addresses the limitation in this way. Each step in that chain needs to be present.

5. Why alternatives are insufficient. A standard wheelchair won't work because of X. A manual wheelchair won't work because of Y. A less expensive option won't address the limitation because of Z. Anticipating the reviewer's question — "why can't they use something cheaper?" — and answering it in the letter is one of the things that distinguishes strong letters from weak ones.

6. The expected outcome. What will the equipment allow the patient to do that they can't currently do, or what will it prevent that's currently happening? "This equipment will allow the patient to safely transfer independently, reducing the risk of caregiver injury and preventing the falls she has experienced three times in the past six months."

A letter that contains all six pieces, in plain clinical language, with specifics rather than generalities, is hard to deny. A letter missing two or three of these is the kind that produces an initial denial.

How to ask a provider for one

Most providers will write letters of medical necessity when asked, but the quality of what gets written depends a lot on how the request is made. A few practical suggestions:

Ask early, not late. Letters take time to write properly, and providers' schedules are full. Asking during a visit specifically scheduled to discuss the equipment is different from catching the provider in the hallway after a different appointment. If a piece of equipment is being considered, raising it as the agenda for a specific visit gets more attention than adding it on at the end.

Be specific about what equipment is being prescribed. The provider can't write a strong letter without knowing what they're justifying. If the equipment supplier has recommended a specific configuration, bring that information. If a seating evaluation has been done, bring the evaluation report. The provider's letter then references the supplier's recommendation and the evaluation, which strengthens it.

Share the functional details. Providers see patients in brief windows in office settings. They may not know what daily life looks like at home. Tell them: how far can you walk in your kitchen before resting? Can you get to the bathroom at night without help? Have you fallen, and if so when? These details, in your words, end up in the letter when the provider knows them.

Ask for a draft you can review. Some providers will share the letter before submitting it, others won't. It's reasonable to ask. If you see a draft and notice that something important is missing — a specific functional limitation, a specific feature of the equipment, the reason a cheaper alternative won't work — you can ask for it to be added before submission.

If the provider doesn't usually write these letters, ask if they can refer to someone who does. Some primary care providers write letters routinely; others rarely do. For complex equipment requests, a specialist who works with the same equipment frequently — a physiatrist, a rehabilitation medicine doctor, a neurologist — often writes more useful letters than a primary care provider. The right specialist for your situation may already be involved in your care or may be one referral away.

What to do when the first letter isn't strong enough

If a claim is denied and the denial letter cites insufficient medical necessity documentation, the first letter probably wasn't strong enough. This is fixable. A few paths forward:

Request an addendum. The provider can write a supplemental letter that addresses the specific concerns raised in the denial. If the denial says "no documentation of inability to ambulate," the addendum can add that. If the denial says "alternative equipment not considered," the addendum can address why alternatives won't work.

Get a seating evaluation, functional evaluation, or specialist consultation. For wheelchair claims especially, a formal seating evaluation by a certified specialist often produces documentation that a primary care provider can't generate. The evaluation becomes a supporting document for an appeal.

Switch providers if necessary. If the prescribing provider isn't able or willing to write a strong letter, sometimes a referral to a different provider — usually a specialist — solves the problem. This isn't an abandonment of the existing relationship; it's recognizing that different providers have different roles.

Use the appeal process. Insurance denials can be appealed, and appeals frequently succeed when supported by a stronger letter and additional documentation. We cover the appeals process in more depth in a separate article (see, Letters of Medical Necessity article).

A note on advocacy

For complex cases, getting a strong letter sometimes requires advocacy that goes beyond the patient or family. Hospital social workers, case managers, Centers for Independent Living, disability advocacy organizations, and patient advocates exist in part to help navigate this kind of situation. They know which providers in the area write strong letters, what the local insurance reviewers tend to scrutinize, and what successful appeals have looked like in similar cases.

If you've hit two denials and aren't sure what to do next, reaching out to an advocate is reasonable. Most are happy to help, and many of their services are free.

How BSILS fits

BSILS doesn't write letters of medical necessity — that requires a licensed provider with a clinical relationship to the patient. But we do work alongside people who are navigating equipment requests, and we know how often the letter is what determines the outcome.

When BSILS receives an inquiry from someone whose equipment request was denied for insufficient documentation, we try to help them understand what the denial actually means and what the next step looks like. Sometimes that's pointing them toward a Center for Independent Living, sometimes toward a specialist who can write a stronger letter, sometimes toward an attorney for a particularly complicated case. We can also occasionally provide donated equipment as an interim solution while a longer insurance process plays out.

If you're working on a letter of medical necessity and want to talk through what's in it, contact us. We can't write the clinical content, but we can often help you think about what to ask the provider for.

This article provides general information about letters of medical necessity, insurance documentation, and Montana resources. It is not legal, medical, financial, or insurance advice for your specific situation. Insurance rules, documentation requirements, and provider practices vary. For decisions about your case, please consult your healthcare provider, your insurance company, or a qualified benefits advocate. If you are not sure where to start, contact us — we are happy to help you find the right local resource.