How to write a letter of medical necessity

A letter of medical necessity explains why a patient needs a specific item or service and why a cheaper alternative will not do. It is often requested for equipment, therapy, out-of-network care or a medicine outside a formulary. ClearPass drafts it from the visit note so the facts in the letter match the facts in the chart.

What the letter has to prove

Reviewers of these letters are usually not specialists in your field. They check whether the document shows a clear chain: a diagnosis, a functional problem caused by it, a specific item that addresses that problem, and a reason the standard or cheaper option is not enough. When any link is missing, the letter reads as a preference rather than a need.

The strongest letters are specific. They say how far the patient can walk, what they cannot do at home, which device or drug was tried and what happened. General statements such as 'the patient would benefit' carry little weight on their own.

• Diagnosis with onset and how it was confirmed.
• Measurable impairment: range of motion, strength grade, falls, distance walked, scores on validated tools.
• Alternatives already tried or considered, and why each is unsuitable.
• The exact item or service requested, with the specification that matters clinically.
• Expected benefit and the risk of not providing it, such as falls, admission or loss of independence.
• How long the need is expected to last.

A structure that works for most requests

1. Opening line. Who you are in relation to the patient and exactly what you are requesting.
2. Clinical background. Diagnosis, relevant history and the current examination findings.
3. Functional impact. What the condition prevents the patient from doing, with numbers where possible.
4. Alternatives. What else was tried or considered, with dates, and why it did not meet the need.
5. The request and its rationale. Why this specific item or service is appropriate, and what it is expected to achieve.
6. Closing. A plain restatement of the request and the codes that support it.

Example

I am requesting a custom-moulded ankle-foot orthosis for [Patient initials], aged 63, whom I have followed since an ischaemic stroke seven months ago.

Diagnosis: Foot drop, right foot (M21.371), following cerebral infarction.

On examination, right ankle dorsiflexion is 1/5 with a steppage gait. The patient has had three falls at home in the last two months, one causing a wrist injury.

An off-the-shelf orthosis was used for 10 weeks. It caused pressure areas over the lateral malleolus on two occasions because of marked spasticity and a fixed varus position, and was stopped.

A custom device is needed to hold the ankle in a neutral position, prevent further falls and allow the patient to continue walking independently indoors. The need is expected to be long term.

Notice what the excerpt does not do: it does not describe the patient's character, promise an outcome or rely on adjectives. Each claim can be checked against the chart.

Why these letters get turned down

• The functional problem is described in words only, with no measurement.
• The cheaper option is dismissed without saying it was tried or why it cannot work.
• The item requested is vague, so the reviewer cannot tell why the specific version matters.
• The diagnosis code does not match the problem the letter describes.

ClearPass drafts the letter from the note you already wrote or transcribed. Choose Concise, Standard or Detailed, and it adds ICD-10 codes and procedure codes where your system uses them. If a fact a reviewer will look for is not in the note, it asks you rather than guessing. You read and edit every letter before it goes anywhere. For requests tied to a specific test or procedure, the prior authorization letter page covers the same process.

What ClearPass does not do

• It does not replace your judgement. Every note is an AI draft that you review and correct before it is used.
• It is not a medical device and does not make clinical decisions. It is a documentation aid.
• It does not connect to your EMR. The note is copy-ready text that pastes into any system.

Privacy

Clinical note content is not stored on ClearPass servers: it is processed to write the note, then discarded. Consultation audio is transcribed and discarded, never stored. Your note history stays in your browser, on your device, and you choose how long it is kept. Common identifiers are removed from typed and transcribed text before it reaches the AI; that is a best-effort safeguard, so leave names, ID numbers and file numbers out where you can. Processing goes through the AI providers named in our Privacy Policy, which sets out exactly what each one receives and how long it keeps it. ClearPass does not sign HIPAA business associate agreements today.

Questions

Related

• Prior authorization letters written from the visit itself
• Prior authorization for physiotherapy and extra sessions
• Appealing a 'not medically necessary' denial
• An AI medical scribe for physical medicine and rehabilitation