Letter of Necessity Template With Examples

What is a Letter of Medical Necessity?

A letter of medical necessity (LMN) is a document a clinician fills out to verify that a clinical service or treatment is medically required. Insurers and FSA/HSA programs require it to determine eligibility for coverage of treatments, procedures, or items.

In this article, we will cover the role of a letter of medical necessity, practices in the United States and other countries, and how to document a letter of medical necessity.

The Role of a Letter of Medical Necessity

The role of a letter of medical necessity is to help secure timely, reliable coverage approvals. It strengthens the case for care and reduces delays for patients. These letters provide a significant impact on care proponents, including:

Improves Quality of And Patient Access To Care

Letters of medical necessity that include thorough clinical detail lead to faster approvals and help patients access the care they need. Initial denials can be overturned successfully on appeal through complete data submission. As a result, patients can access quality care faster and remain on optimal treatment paths.

Accelerates Operational Efficiency

Mid-sized practices operate with limited administrative capacity. Prior authorization burden drains clinical capacity and pulls decisions away from what is clinically right for the patient. This makes systematic tracking of medical necessity letters crucial, as it surfaces hidden gaps and patterns.

Reduces Administrative Burden

Prior authorization supported by the letter of medical necessity typically consumes 20 minutes of staff time in primary care settings. Even with electronic health records, the process remains time-intensive and adds to routine administrative workload.

Across practices, this effort accumulates into hours of work that sit outside direct patient care. Administrative costs associated with prior authorization can outweigh the intended efficiencies, placing additional strain on care teams and practice operations.

Heidi is designed to help reduce administrative burden. Watch to learn more how it helps ensure your clinical justification is clear, complete, and ready for submission wherever care is delivered.

Letters of Medical Necessity: FSA in the US vs. Global Practices

Letters of medical necessity in the United States help document why a specific service, treatment, or expense is clinically required. When authored by a clinician, they support coverage decisions and can allow certain expenses, not typically eligible, to be reimbursed through FSAs, HSAs, or HRAs.

Globally, requirements vary. For example, the UK does not require a letter of medical necessity for treatment.

Here are the differences per location:

Medical Necessity and Prior Authorization in the US

Private insurance and tax-advantaged benefit accounts shape the American healthcare system. Insurers enforce prior authorization (PA) independently. Most high-cost physician-administered drugs require prior authorization, often with step therapy.

Even in government-aligned plans, medical necessity requirements are applied closely.

The letter of medical necessity has become a clinician-authored document used to navigate insurer barriers to care. Reform is moving forward, with faster prior authorization timelines and policy changes underway.

The multi-payer structure remains, and so does the need to demonstrate medical necessity clearly.

Clinical Guidelines and Medical Necessity in the UK (NHS)

In the UK, letters of medical necessity are not typically required in the same way. The NHS operates under a single-payer model, where treatment decisions are guided by national standards set by NICE. This means that the framework for what’s clinically appropriate is already built into the system.

For most care, clinicians won’t be writing letters to justify treatment to insurers; they rather follow established clinical pathways. This reduces administrative burden and allows more time to be spent on direct patient care. That said, it’s worth knowing that prior approval does still exist for certain high-cost drugs and devices.

Medical Necessity and PBS Pathways in Australia

Australia’s healthcare system follows the PBS’ structure. Authority Required benefits under the PBS necessitate prior approval from Services Australia, and prescribers must submit detailed applications before dispensing certain medications. These applications includes clinical information.

How Medical Necessity Is Documented Across Global Care Systems

Medical necessity is managed across different healthcare systems. For example, in Canada, provincial government bodies define what is "medically necessary" based on evidence-backed guidelines. Countries such as Germany and France, mandatory insurance systems operate within regulated benefit frameworks that guide access to care.

In publicly funded systems, medical necessity is typically governed through national or regional clinical guidelines and coverage pathways. In multi-payer systems, such as the US, it is more often assessed through insurer-specific criteria and prior authorization processes. Across all systems, clear clinical documentation remains essential to justify care and support access.

Daily, Dr. Aman Khanna, an ENT surgeon, witnesses the standard of care in practice. This is particularly evident as he addresses the inefficiencies he faces with the documentation process. "Before Heidi, we were just typing notes and dictating letters. It’s what I’ve done in the NHS for years, but it’s time-consuming."

Heidi changed it all. Now, Heidi saves him 7-8 minutes per patient, resulting in less mental strain and a better patient focus. His experience proves that less time spent on documentation improves care quality and allows clinicians to stay present with patients.

"The mental burden is just gone. I feel more relaxed with my private patients because I don’t have to think about the documentation."

How To Document A Letter Of Medical Necessity

Mastering the documentation of a medical necessity letter is essential for clinicians. This necessity stems from several pressures: the increasing administrative burden of prior authorization, the direct correlation between documentation quality and patient care, and the proven influence of thorough clinical notes on favorable approval and appeal outcomes.

Here is how you can document letters of medical necessity better:

Step 1: Establish Patient History and Clinical Context

Document the onset, duration, and progression of the condition. Do not forget to mention prior diagnostic workup and findings. Include prior investigations and note any comorbidities that may affect treatment decisions.

Step 2: Document Treatment History

List the names, doses, and durations of all prior treatments tried. Clearly document whether treatment was ineffective, not tolerated, or clinically inappropriate, so the reasoning is easy to follow.

Step 3: Describe Functional Impact

Explain how the condition affects the patient’s daily life and overall functioning. Where possible, support this with objective measures such as functional scores, laboratory results, or imaging findings.

Step 4: Cite the Evidence Base

Reference specialty society guidelines, clinical pathways, or peer-reviewed literature that supports the requested intervention. Complete and accurate medical documentation strengthens prior authorization requests for DME and devices.

Heidi Evidence supports the step by surfacing guidelines and peer-reviewed literature with citations that clinicians can open and verify. This makes it easier to reference clinical recommendations accurately, and maintain a clear source trail within the documentation workflow.

Step 5: Add Physician Attestation

Include a clear, signed statement from the treating clinician. This should reflect independent clinical judgment and confirm that the requested service is medically necessary.

Step 6: Ensure Documentation Accuracy

Review the letter against the key elements commonly assessed by payers. They include:

• Confirmed diagnosis with appropriate coding
• Functional limitations and symptom severity
• Evidence of prior treatment and outcomes
• Clear rationale for the requested service
• Expected impact if the service is not provided

Complete and accurate documentation supports smoother review and reduces the need for follow-up clarification. This way, clinician oversight remains essential to ensure patient safety and documentation quality.

Step 7: Using Heidi To Support Letter Preparation

Heidi can support documentation by organizing clinical details captured during the encounter into a clear, structured format. This includes diagnosis, treatment history, functional impact, and clinical reasoning.

When used alongside Heidi Evidence, clinicians can reference relevant guidelines during the consultation or documentation process. This helps ensure the letter reflects current clinical standards and is easier to review.

Consistent, well-structured documentation supports clearer letters of medical necessity, helping reduce rework and improve access to care.

Free Letter of Medical Necessity Templates