Letters of Medical Necessity (LMNs)LMN Basics

LMN Requirements

A Letter of Medical Necessity (LMN) is only as useful as the documentation it contains. HSA and FSA administrators — and the IRS rules they enforce — have specific expectations for what an LMN must address. This article explains what those requirements are, how Truemed’s LMNs are structured to meet them, and what to do if your documentation is questioned.

What an LMN must establish

Under IRS Section 213(d), a qualifying medical expense must be for the “diagnosis, cure, mitigation, treatment, or prevention of disease, or for the purpose of affecting any structure or function of the body.” An LMN is the document that establishes this connection for a specific purchase.

To satisfy plan administrators, an LMN must demonstrate three things:

  1. A diagnosed condition — There must be a specific, documented health condition. A general desire to improve fitness or sleep is not sufficient. The condition must be identifiable and clinically documented.
  2. A treatment recommendation — The product or service must be specifically recommended as part of the treatment plan for that condition.
  3. A link between the two — The LMN must explain why this product, for this condition, for this patient, is medically necessary — not merely beneficial or convenient.

Required elements of a valid LMN

A well-structured LMN includes the following:

Provider information

  • Full name, title, and professional credentials
  • National Provider Identifier (NPI) number and/or state medical license number
  • Address and contact information
  • Date the letter was issued

Patient information

  • Patient’s full name

Diagnosis

  • The specific condition being treated, mitigated, or managed
  • ICD-10 code(s) where applicable
  • A brief description of how the condition affects the patient

Treatment recommendation

  • The specific product or service being recommended
  • Relevant details: frequency of use, duration, or any relevant device specifications
  • Why this particular product is the appropriate intervention

Medical necessity justification

This is the most critical section. It must explain:

  • Why the product is clinically necessary for this patient’s specific condition (not just generally helpful)
  • How it is expected to improve function, reduce symptoms, or prevent complications
  • Any supporting clinical rationale, research, or guidelines that back the recommendation
  • Why the product would not be appropriate as a purely general purchase

Signature and credentials

  • Provider’s full name, title, and credentials
  • Provider’s signature
  • Date of signature

How Truemed’s LMNs meet these requirements

When you complete Truemed’s clinical intake survey, your responses are reviewed by an independent, licensed clinician on Truemed’s provider network. If your purchase qualifies, the clinician issues an LMN that:

  • Is written on official clinical letterhead with the provider’s full credentials and NPI
  • States your specific diagnosed condition and relevant ICD-10 code(s)
  • Names the exact product and merchant for which it was issued
  • Includes a clinical rationale connecting your diagnosis to the recommended product
  • Is signed and dated by the issuing clinician

This is why the intake survey asks for health information, the clinical detail you provide is what enables the provider to write documentation that meets administrator standards, not just one that states “this is necessary.”

Common reasons an LMN is questioned or rejected

Even valid LMNs can run into problems during the reimbursement process. The most frequent issues:

Too vague. A statement like “this treatment will improve the patient’s health” is not sufficient. The LMN must connect the product to the patient’s specific diagnosis. Administrators expect to see a clear clinical chain: condition → symptom impact → recommended product → expected outcome.

Diagnosis doesn’t clearly apply to the product. If the health condition listed on the LMN doesn’t have an obvious clinical connection to the product purchased, an administrator may flag it. For example, a diagnosis focused on one area of the body may not provide sufficient justification for a product that addresses a different condition entirely.

Missing required fields. LMNs without a provider signature, credentials, NPI, or official letterhead are commonly returned or rejected outright. These are administrative requirements, not clinical ones — but they carry equal weight with most administrators.

General wellness framing. An LMN that reads as a general endorsement of healthy behavior rather than a treatment recommendation for a specific condition is likely to be denied. The IRS standard is medical necessity, not lifestyle support.

Lack of specificity on the product. If the LMN references a broad product category (e.g., “exercise equipment”) rather than the specific product purchased, some administrators will not accept it.

If your LMN is questioned

If your plan administrator requests additional documentation or questions your LMN, contact Truemed at support@truemed.com. Include:

  • Your order details and the merchant name
  • The specific reason or language your administrator used when questioning the LMN
  • Any denial or development letter you received

Truemed can review your documentation, clarify what the administrator is looking for, and in some cases work with the clinical provider to provide supplemental information. See Denied Claims for guidance on the appeal process.