What is a letter of medical necessity?

A letter of medical necessity (LMN) is a formal document written by a healthcare provider explaining why a specific treatment, medication, equipment, or service is medically necessary for a patient's condition. It provides clinical justification to support insurance coverage.

When is a medical necessity letter required?

Medical necessity letters are typically required for durable medical equipment (DME), non-formulary medications, cosmetic procedures with medical indication, experimental treatments, home health services, and other services requiring additional justification beyond standard authorization.

What should be included in a medical necessity letter?

Key elements include patient diagnosis with ICD-10 codes, detailed description of the condition, functional limitations and impact on daily life, specific item or service requested, clinical rationale for necessity, expected benefits, risks of denial, and provider credentials and signature.

How is a medical necessity letter different from prior authorization?

Prior authorization is a standard insurance approval process for scheduled services. A medical necessity letter provides additional clinical justification, often used when standard PA is denied, for DME requests, or when services fall outside typical coverage criteria.

What tips improve medical necessity letter approval rates?

To improve approval rates: use specific diagnosis codes and medical terminology, cite clinical guidelines (ACR, AUA, ACOG), quantify functional limitations with objective measures, document failed alternatives and contraindications, include relevant lab results and imaging, and address specific insurance criteria. Keep letters concise but comprehensive, typically 1-2 pages.

Medical Necessity Letter Template - LMN Documentation

Administrative — Medical Necessity Letter Template

Administrative Utilization Management Updated: 11/7/2025

The Medical Necessity Letter Template is an essential resource for physicians and healthcare providers writing letters of medical necessity (LMN) to support insurance coverage for medications, durable medical equipment (DME), procedures, or services. This template provides the structured format and clinical language required by insurance companies to justify medical necessity for treatments that may require additional documentation beyond standard prior authorization. The template includes patient demographic and clinical information, detailed clinical rationale explaining why the requested item or service is medically necessary, documentation of functional limitations and impact on daily activities, supporting clinical evidence and guidelines, expected outcomes and benefits, risks of not providing the service, and professional attestation. This template streamlines the LMN process, ensures inclusion of all required elements to maximize approval rates, supports compliance with insurer requirements, and protects provider time by standardizing documentation. The structured format is adaptable for DME requests (wheelchairs, CPAP machines, home health equipment), medication coverage, procedure authorizations, and other services requiring medical necessity justification. Ideal for busy clinical practices, specialty care providers frequently dealing with insurance requirements, and administrative staff responsible for completing medical necessity documentation.

Letter Header

Provider name, credentials, practice name
Address, phone, fax, NPI
Date

Patient Information

Patient name, DOB, insurance ID
Diagnosis: [Primary diagnosis with ICD-10 code]

Requested Item/Service

[Specific item or service requested]
[Quantity, frequency, duration if applicable]

Clinical Rationale for Medical Necessity

Patient's condition: [Detailed description]
Functional limitations: [Impact on daily activities, mobility, safety]
Why this item/service is necessary: [Clinical justification]
Expected benefits: [How this will improve patient's condition or function]
Risks of not providing: [Consequences of denial]

Supporting Clinical Evidence

Clinical guidelines: [Relevant guidelines supporting request]
Evidence-based medicine: [Studies or evidence supporting use]
Functional assessment: [Documented functional limitations]

Provider Attestation

I certify that [item/service] is medically necessary for this patient based on [clinical reasons]. This request is consistent with generally accepted standards of medical practice.

Provider Signature

[Signature, credentials, date]

Administrative — Medical Necessity Letter Template

Template