A letter of medical necessity is a document from a treating physician or licensed healthcare provider that explains why a specific treatment, service, or piece of equipment is essential for a patient’s care. Whether you’re a provider writing one for a patient or a patient helping to draft one for your doctor’s review, the letter needs to accomplish one thing: convince an insurance company that the requested service is not optional. The difference between approval and denial often comes down to how well the letter connects a patient’s diagnosis to the specific request, supported by clinical evidence.
What the Letter Must Include
Every letter of medical necessity shares a core structure, regardless of whether it’s for a medication, a piece of equipment, home health care, or a surgical procedure. The essential elements are:
- Patient identifiers: Full name, date of birth, member ID, and policy number.
- The specific request: Name the exact treatment, service, supply, or equipment being requested.
- Documented diagnosis: The patient’s condition, stated clearly and linked directly to the request.
- Medical rationale: A written explanation of why this particular service or item is necessary for this particular patient.
- Supporting clinical evidence: Test results, imaging, medical records, or other documentation that backs up the rationale.
- Failed alternatives: Evidence that less invasive or less costly treatments were attempted and didn’t work.
- Expected outcomes: What the treatment is likely to achieve, or what happens if the patient doesn’t receive it.
- Provider credentials: The provider’s signature, printed name, license number, state of licensure, and contact information.
Missing any one of these elements is a common reason for denial. Insurance companies compare the letter against their own internal medical policies, and if the documentation doesn’t address each criterion those policies outline, the claim gets rejected regardless of how legitimate the need is.
How to Structure the Letter
Use a standard business letter format. At the top, include the date, the insurance company’s name and address, and a “Re:” line with the patient’s name, date of birth, and member ID. Address it to “Dear Claims Representative” unless you have a specific contact name (which you will if you’re responding to a denial).
Open with a single sentence identifying yourself, your relationship to the patient, and what you’re requesting. For example: “I am writing on behalf of my patient, [name and policy number], to request that [insurance company] approve coverage for [specific treatment or item] in relation to their [diagnosis].” This immediately tells the reviewer what the letter is about and who it’s for.
The body of the letter should follow a logical sequence. Start with the patient’s diagnosis and relevant medical history. Then describe the clinical course: how long the condition has persisted, whether it’s worsening or stable, and what functional limitations the patient experiences in daily life. Next, explain what treatments have already been tried and why they were inadequate or ineffective. Only then should you present your recommendation, explaining why the requested service is the appropriate next step and what outcome you expect it to produce. Close by noting that supporting clinical evidence is attached, and sign with your full credentials.
Keep the tone factual and direct. Emotional appeals don’t move insurance reviewers. Specific clinical detail does.
Documenting Failed Alternatives
This is where many letters fall short. Insurance companies typically require evidence that less invasive or less costly treatments were attempted before they’ll approve something more intensive or expensive. Simply stating “previous treatments failed” isn’t enough. You need to specify which treatments were tried, for how long, at what dosage or frequency, and what the measurable result was.
For example, if you’re requesting approval for a surgical procedure, the letter should detail the conservative measures that came first: physical therapy (how many weeks, how many sessions per week), medications (which ones, at what doses, for how long), injections, bracing, or other interventions. For each, note the outcome. Did the patient’s pain remain at the same level? Did their range of motion fail to improve? Did imaging show continued deterioration despite treatment? These specifics turn a generic claim into a persuasive one.
Writing for Durable Medical Equipment
Letters requesting coverage for equipment like wheelchairs, prosthetics, hospital beds, or CPAP machines have additional requirements. The Centers for Medicare and Medicaid Services expects documentation of the patient’s specific functional limitations: what they cannot do, how the equipment addresses those limitations, and how the condition affects their daily activities.
Include the duration of the condition, whether it’s improving or worsening, the patient’s prognosis, and any past experience with related equipment. If you’re requesting a replacement device, document the reason. Acceptable reasons include changes in the patient’s weight or physical condition, irreparable damage to the current device, or repair costs exceeding 60 percent of replacement cost. A new order from the treating provider is required for replacements.
For home health care specifically, many payers require that the patient meet “homebound” criteria. This means the patient has trouble leaving home without assistance (a cane, wheelchair, walker, or help from another person), that leaving home isn’t recommended due to their condition, or that doing so requires a major effort. The letter should describe these limitations in the patient’s own context rather than just checking a box.
Writing for Insurance Appeals
If a claim has already been denied, the letter of medical necessity takes on a different structure. Address it to the appeals analyst named in the denial letter, and send it certified mail with return receipt requested. If the patient needs the treatment urgently, also fax or email it and request an expedited review.
Open by identifying the patient, the plan, and the specific denial you’re appealing. Quote the insurance company’s own language from the denial letter and attach it. Then systematically dismantle the stated reason for denial. The University of Rochester Medical Center recommends a three-part approach: first, establish that the treatment is medically necessary by describing the patient’s condition and why the treatment team recommends it. Second, establish that the treatment is a covered benefit by quoting the plan’s own member handbook or Evidence of Coverage document. Third, explain what will happen to the patient if they don’t receive the treatment.
If the denial was for an out-of-network provider, show that the plan’s network did not include the type of provider needed, that in-network providers were more than 30 miles away, or that wait times for in-network appointments were unreasonably long. For mental health or substance abuse treatment, federal parity laws require insurers to cover these services the same way they cover medical and surgical care, and the letter should reference that standard if relevant.
Special Considerations for Off-Label Medications
When a medication is prescribed for a use not listed on its FDA-approved label, insurance companies apply stricter standards. Medicare Part D, for instance, only covers off-label drug use if the drug is identified as safe and effective for that use in one of three officially recognized drug reference databases. Only one of these references needs to support the off-label use for coverage to apply. The letter should cite which reference supports the prescribed use and include relevant peer-reviewed literature when available.
For non-Medicare plans, the requirements vary, but the principle is the same: the letter must present published evidence that the drug is effective for the condition being treated, not just the provider’s clinical opinion.
Common Reasons Letters Get Denied
Insurance companies deny claims for medical necessity when the submitted documentation doesn’t meet the specific criteria outlined in their internal policies. The most frequent problems are vague language (“patient needs this treatment”), missing clinical evidence, failure to document why alternatives didn’t work, and not connecting the diagnosis directly to the requested service. A letter that says “the patient has chronic back pain and needs a motorized wheelchair” will be denied. A letter that describes specific spinal pathology, documents failed physical therapy and medication trials, details the patient’s inability to self-propel a manual wheelchair due to upper extremity weakness confirmed on examination, and explains how the motorized wheelchair restores functional independence has a far better chance.
Another common issue is timing. Some payers require that a physical exam was performed within a specific window before the request. For home health care, the Department of Labor requires an exam within 60 days. For other ancillary services, the window may be six months. Check your payer’s requirements before submitting.
Who Can Sign the Letter
The letter must come from a licensed healthcare provider. For most insurance claims, this means the treating physician. For flexible spending account reimbursements, IRS rules allow any licensed healthcare provider to certify medical necessity. For durable medical equipment, the order and supporting documentation must come from the treating practitioner. If the letter involves a specialist recommendation, having both the specialist and the primary care provider sign strengthens the case, particularly for appeals where the denial letter questions whether the treatment team supports the request.