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Understanding Letter of Medical Necessity (LMN)
A Letter of Medical Necessity is a document from your doctor that explains why a particular product, service, or treatment is medically necessary for your specific condition. It's often required for certain HSA/FSA expenses.
What is a Letter of Medical Necessity?
A Letter of Medical Necessity (LMN) is a formal document written by a licensed healthcare provider that:
- •Diagnoses a specific medical condition you have
- •Explains why a particular treatment, product, or service is medically necessary
- •Prescribes or recommends the specific item or service
- •Documents that the expense is for treatment (not general health or cosmetic purposes)
When Do You Need an LMN?
You typically need a Letter of Medical Necessity for items and services that:
Items that are only eligible when used to treat a specific diagnosed medical condition (not for general health)
Products or services that could be for personal use or medical treatment (e.g., gym membership, special diet)
When your HSA/FSA administrator asks for additional substantiation for a claim
For borderline expenses where you want documentation in case of an IRS audit
Common Items That May Require an LMN
Requires LMN to show it treats a specific diagnosed medical condition (e.g., chronic pain, injury recovery)
Must be prescribed for a specific medical condition (e.g., obesity, heart disease, diabetes)
For physical therapy or treatment of a specific condition (e.g., arthritis, injury rehabilitation)
Must be prescribed to treat a diagnosed deficiency or medical condition
Must treat a specific diagnosed condition (e.g., celiac disease, PKU) and be substantially different from normal diet
For treatment of allergies, asthma, or other respiratory conditions
Must treat obesity as a diagnosed disease or another specific condition
Generally eligible, but some plans may require LMN for substantiation
What Should an LMN Include?
A valid Letter of Medical Necessity should include the following components to satisfy IRS requirements:
Full name, date of birth, and contact information
Doctor's name, credentials, medical license number, and contact details
Specific diagnosis (with ICD-10 code if possible) requiring treatment
Explanation of why the item/service is medically necessary for treating the condition
Specific product, service, or treatment being recommended
How long the treatment will be needed (ongoing, 6 months, etc.)
Original signature and date of issuance
Professional letterhead (recommended but not always required)
How to Get a Letter of Medical Necessity
Follow these steps to obtain an LMN from your healthcare provider:
Determine if the expense you want to claim requires an LMN. Check with your HSA/FSA administrator or use our search tool.
Book an appointment with your physician (primary care doctor or specialist treating your condition).
Explain the item or service you need and how it relates to your medical condition. Be specific about the treatment.
Ask your doctor to provide a Letter of Medical Necessity on their letterhead. You can provide them with the required components.
Ensure the letter includes all required components: diagnosis, medical necessity, prescribed treatment, and duration.
Make several copies of the LMN. Keep one with your receipts, submit one with your HSA/FSA claim, and keep a digital backup.
Sample LMN Template
[Physician's Letterhead]
(Doctor's Name, Credentials, Address, Phone)
Date: [Current Date]
RE: Letter of Medical Necessity for [Patient Name]
DOB: [Date of Birth]
To Whom It May Concern:
This letter is to certify that [Patient Name] is under my care for [Diagnosis/Medical Condition] (ICD-10: [Code]).
As part of the treatment plan for this condition, I am prescribing/recommending [Specific Item/Service/Treatment]. This [item/service] is medically necessary because [explain how it treats the condition and why it's necessary].
The patient will require this [item/service] for [duration: ongoing/6 months/1 year/etc.] to effectively manage and treat their condition.
If you have any questions regarding this recommendation, please contact my office at [phone number].
Sincerely,
[Physician Signature]
[Physician Name, Credentials]
[Medical License Number]
Important Reminders
IRS Guidance & Citations
Substantiation requirements for health FSAs and other employer-provided health coverage
Medical and Dental Expenses - Defines qualified medical expenses and special circumstances
Health Savings Accounts and Other Tax-Favored Health Plans