What Physicians Consider Before Writing a Medical Necessity Letter
Written by YiQiu Hu, NMD
Arizona-licensed naturopathic physician and virtual concierge medicine provider
Published August 2026 | Medically reviewed August 2026
A letter of medical necessity can help explain why a particular medication, treatment, diagnostic test, medical device, therapy, or healthcare service is clinically appropriate for an individual patient.
But a physician does not simply write a letter because a patient, insurance company, employer, or other organization asks for one.
Before supporting medical necessity, the physician needs to understand the medical condition involved, review the available evidence, determine what has already been tried, consider appropriate alternatives, and decide whether the requested service can be supported by independent clinical judgment.
This is an important distinction. A medical necessity letter is a professional medical opinion, not simply an administrative formality and not a guarantee that an insurance company or other organization will approve the request.
If you are unfamiliar with physician documentation in general, our complete guide to medical documentation explains how medical forms, letters, certifications, and professional opinions are evaluated.
What Is a Letter of Medical Necessity?
A letter of medical necessity is documentation from a physician or other qualified healthcare professional explaining why a specific healthcare item or service is medically appropriate for a particular patient.
Depending on the situation, the requested service might involve:
A prescription medication
Diagnostic testing
Imaging
Physical or rehabilitative therapy
Durable medical equipment
Medical supplies
A procedure or treatment
Specialized care
A particular frequency or duration of treatment
An insurance appeal after a service has been denied
The exact meaning of medical necessity can depend on the organization reviewing the request.
For example, Medicare generally limits coverage to services that meet applicable requirements and are considered reasonable and necessary for diagnosing or treating an illness or injury. Commercial insurance companies may use their own benefit terms, clinical policies, formularies, utilization-management rules, and coverage criteria.
For that reason, a physician may believe that a treatment is clinically appropriate while an insurance plan still determines that it does not meet the plan's specific coverage requirements.
A Medical Necessity Letter Is More Than a Diagnosis
One of the most common misconceptions is that having a diagnosis automatically establishes the medical necessity of a particular treatment.
It usually does not.
Two patients can have the same diagnosis but require very different treatment plans based on factors such as:
Severity of the condition
Duration of symptoms
Functional impairment
Other medical conditions
Previous treatment
Medication response
Contraindications
Treatment goals
Individual risks and benefits
A physician therefore has to connect the diagnosis to the specific treatment, test, medication, device, or service being requested.
For example, simply stating that a patient has chronic back pain provides relatively little information about why a particular imaging study, procedure, medication, or medical device is necessary.
A stronger medical explanation describes the clinical circumstances that make the requested intervention appropriate for that individual patient.
1. What Is Actually Being Requested?
Before evaluating medical necessity, the physician first needs to know exactly what the receiving organization is asking for.
A patient may say, “My insurance needs a letter,” but the actual requirements can be much more specific.
The physician may need to determine:
Who is requesting the documentation
What treatment, medication, test, or service is being requested
Whether there is an official form
Whether prior authorization is required
Whether the request follows an initial denial
What clinical questions must be answered
Whether a specific diagnosis code or procedure is being reviewed
Whether supporting medical records are required
Where and how the documentation must be submitted
Whether there is a deadline
Providing the actual denial letter, prior-authorization request, benefit information, or documentation instructions can be extremely helpful.
Patients requesting physician documentation can review our patient guide to requesting medical documentation before their appointment.
2. Is the Diagnosis Adequately Supported?
A physician generally needs a reasonable clinical basis for the condition being used to justify the request.
Depending on the medical issue, supporting information may include:
Medical history
Current symptoms
Physical examination findings
Laboratory results
Imaging studies
Specialist evaluations
Pathology findings
Previous diagnostic testing
Hospital or emergency-department records
Treatment records
Previous physician assessments
Not every condition requires an abnormal laboratory test or imaging finding. Many diagnoses are primarily clinical.
However, the physician should still be able to explain how the diagnosis was reached and why it is relevant to the requested service.
If important information is missing, additional evaluation may be necessary before a medical necessity opinion can be provided.
3. How Severe Is the Condition?
The existence of a diagnosis is only part of the evaluation.
The physician may also consider the severity and persistence of the patient's symptoms.
Relevant questions may include:
How long has the condition been present?
Are symptoms improving, stable, or worsening?
How frequently do symptoms occur?
How intense are they?
Are there objective abnormalities?
Does the condition interfere with normal activities?
Has it resulted in emergency visits, hospitalization, or other complications?
Are symptoms affecting sleep, mobility, concentration, nutrition, employment, or other important functions?
This information helps establish why treatment is needed and how urgently it may be needed.
4. How Does the Condition Affect the Patient's Function?
Functional impairment can be particularly important when determining medical necessity.
A physician may evaluate whether the condition interferes with a patient's ability to:
Walk
Stand
Sit
Lift
Exercise
Sleep
Eat
Concentrate
Perform personal care
Complete household activities
Work
Attend school
Participate in rehabilitation
Perform other medically relevant activities
For some treatments, the degree of functional limitation may help distinguish between an intervention that is merely optional and one that may materially improve the patient's health or ability to function.
Functional information should be specific whenever possible.
Instead of simply documenting that a patient “has severe pain,” for example, the record may describe how long the patient can stand, which activities trigger symptoms, what happens during those activities, and how the condition has changed over time.
5. What Treatments Have Already Been Tried?
Treatment history is frequently an important component of a medical necessity evaluation.
The physician may review:
Previous medications
Physical therapy
Home exercise programs
Lifestyle modifications
Medical procedures
Injections
Counseling or behavioral treatment
Assistive devices
Previous surgeries
Specialist recommendations
Other conservative or standard treatments
The important question is not simply whether something was tried.
The physician may also need to know:
How long it was used
Whether the patient followed the treatment adequately
Whether it helped
Why it was stopped
Whether side effects occurred
Whether there was a contraindication
Whether symptoms returned
Whether the treatment was only partially effective
This can become especially important when an insurer requires patients to try one or more alternatives before approving the requested treatment.
6. Why Is the Requested Treatment Appropriate?
This is often the central question in a letter of medical necessity.
The physician needs to establish a logical clinical connection between the patient's condition and the requested intervention.
That reasoning might involve:
The patient's diagnosis
Severity of symptoms
Functional limitations
Examination findings
Diagnostic testing
Previous treatment failures
Treatment intolerance
Contraindications to alternatives
Current medical guidelines
Published evidence
Specialist recommendations
The expected clinical benefit
The explanation should be individualized.
A letter that simply states, “This treatment is medically necessary,” provides far less information than one explaining why it is medically necessary for this particular patient.
7. Are There Reasonable Alternatives?
Physicians also consider whether other reasonable treatment options are available.
This does not mean that every possible alternative must be tried first.
Instead, the physician may evaluate whether an alternative:
Is medically appropriate
Has already been attempted
Is likely to be effective
Is contraindicated
Caused previous adverse effects
Conflicts with another medical condition
Would create an unreasonable medical risk
Is substantially less appropriate for the patient's circumstances
For example, an insurer may recommend a lower-cost medication. The physician may need to explain that the patient previously failed that medication, experienced significant side effects, has a contraindication, or has another clinical reason why the requested medication is more appropriate.
This type of individualized reasoning is often more useful than simply stating that the physician prefers one treatment over another.
8. What Does the Available Medical Evidence Show?
When appropriate, physicians may consider evidence outside of the patient's individual medical record.
That can include:
Evidence-based clinical guidelines
Consensus recommendations
Peer-reviewed medical literature
FDA-approved indications
Specialty-society recommendations
Government coverage guidance
Established standards of care
The amount of external evidence needed depends on the request.
A routine medication authorization may require relatively little supporting literature, while a less common treatment or an appeal involving a disputed indication may require a more detailed explanation of the evidence.
Evidence alone, however, does not determine whether a treatment is appropriate.
Physicians still have to apply that evidence to the individual patient's circumstances.
9. What Could Happen if the Treatment Is Delayed or Denied?
In some cases, the consequences of not receiving the requested treatment are clinically important.
The physician may consider whether a delay or denial could reasonably result in:
Worsening symptoms
Progression of disease
Loss of function
Increased pain
Reduced ability to work or complete daily activities
Emergency care
Hospitalization
Additional treatment
Preventable complications
Reduced likelihood of recovery
These considerations should be described accurately rather than exaggerated.
The goal is to explain the medical implications of the decision, not to create a predetermined administrative outcome.
10. What Duration or Frequency Is Medically Appropriate?
Sometimes the issue is not whether treatment is necessary but how much treatment is necessary.
A request may involve:
Number of therapy sessions
Treatment frequency
Duration of medication
Replacement schedule for equipment
Length of home-health services
Frequency of diagnostic monitoring
Quantity limits for medication
Duration of a particular accommodation or service
The physician should recommend a duration or frequency that can reasonably be supported by the clinical situation.
When the future course is uncertain, the physician may recommend reassessment after an appropriate period rather than certifying an indefinite need.
11. Does the Physician Have Enough Current Information?
A physician's ability to provide a medical necessity opinion depends on the available information.
An evaluation may be necessary when:
The physician has never evaluated the condition
The patient's condition has changed
The available records are outdated
The requested service involves new symptoms
Important testing is missing
The letter requires examination findings
The physician cannot determine the patient's current response to treatment
This is why a physician may sometimes require an appointment before completing a letter.
You can read more in our FAQ, Do I Need an Appointment Before Medical Forms Can Be Completed?.
12. Is the Request Within the Physician's Scope and Expertise?
Not every physician should provide every type of medical opinion.
Some requests may require:
A treating specialist
A surgeon
A psychiatrist or behavioral-health professional
An occupational medicine clinician
A physical or occupational therapist
A rehabilitation specialist
An independent medical examiner
Another professional with specific credentials
A physician may have enough information to document part of the patient's medical history while still determining that another clinician is more appropriate to answer a particular question.
Recognizing those limits is part of responsible medical documentation.
What Records May Help Support a Medical Necessity Letter?
The necessary documentation varies by situation, but helpful information can include:
The organization's request or denial letter
The patient's relevant medical records
Specialist notes
Laboratory results
Imaging reports
Medication history
Previous treatment records
Physical therapy or rehabilitation records
Records documenting treatment failures
Adverse drug reactions
Relevant hospital records
Prior authorization requirements
Insurance correspondence
Previous appeal decisions
Patients generally do not need to provide every medical record they have ever accumulated.
The goal is to identify the information relevant to the medical condition and the specific request.
Our Medical Documentation services page explains the types of records and evaluations that may be necessary before physician documentation can be completed.
Medical Necessity Does Not Mean Guaranteed Insurance Coverage
This distinction is extremely important.
A physician determines whether a treatment or service can be medically supported based on the patient's clinical circumstances.
An insurance company determines whether the service qualifies for payment under the patient's particular health plan.
Those are related questions, but they are not identical.
An insurer may consider:
Plan exclusions
Benefit limitations
Prior-authorization requirements
Network requirements
Step-therapy rules
Formulary restrictions
Coverage policies
Frequency limits
Specific medical-necessity criteria
As a result, a physician may provide a well-supported letter and the insurance company may still deny coverage.
The physician cannot guarantee approval.
When a denial occurs, the physician may sometimes provide additional documentation, clarification, or an appeal if the clinical evidence supports doing so.
Why Might a Physician Decline to Write the Requested Letter?
A physician is not obligated to certify a conclusion that cannot be medically supported.
A request may need to be declined, modified, or delayed when:
There is insufficient evidence of the diagnosis
The physician has not evaluated the relevant condition
Required medical records are unavailable
The requested treatment does not appear medically appropriate
Important alternatives have not been adequately evaluated
The requested statement conflicts with the clinical findings
The documentation asks the physician to certify information they cannot verify
An examination or additional testing is required
The matter requires another medical specialty
The request falls outside the physician's scope of practice
Sometimes the physician may still be able to provide a narrower statement.
For example, the physician may be able to document the patient's diagnosis, treatment history, and symptoms without making a broader medical conclusion that the available evidence does not support.
Accuracy should take priority over producing the exact wording a patient or third party would prefer.
How Patients Can Help Their Physician Prepare an Accurate Letter
Patients can often make the documentation process more efficient by providing complete information from the beginning.
Before requesting a medical necessity letter:
Obtain the actual request, denial, or form from the insurance company or organization.
Find out exactly what information is required.
Provide relevant medical records.
Bring a current medication list.
Identify treatments that have already been attempted.
Explain what happened with each previous treatment.
Provide specialist records when relevant.
Tell the physician about submission deadlines.
Provide the appropriate recipient and submission instructions.
Be prepared for an additional evaluation if the physician needs current clinical information.
For a broader overview of what physicians can complete, see What Types of Medical Documentation Can a Physician Complete?.
What Makes a Strong Medical Necessity Letter?
There is no universal template that works for every situation.
However, a well-supported letter commonly makes the clinical reasoning easy for the reviewer to understand.
Depending on the request, it may address:
The patient's relevant diagnosis
Pertinent medical history
Current symptoms
Severity and functional impact
Relevant examination or testing findings
Treatments already attempted
Response to previous treatment
Why alternatives may not be appropriate
The treatment or service being requested
Why it is medically appropriate
Expected clinical benefit
Potential consequences of not receiving it
Proposed duration or frequency
Supporting medical evidence when relevant
The objective is not simply to make the letter longer.
The objective is to provide the information necessary for another clinician, insurer, or reviewer to understand the physician's reasoning.
Medical Necessity Letters at Ask Dr. Hu
At Ask Dr. Hu, medical necessity requests are evaluated individually.
Depending on the request, the process may include review of medical records, discussion of previous treatments, evaluation of current symptoms, physical examination, diagnostic testing, or review of requirements from the insurance company or other organization.
We provide documentation only when the requested statements can be supported by the available medical information and our independent clinical judgment.
We do not guarantee that an insurer, employer, government agency, benefit administrator, or other third party will approve a request.
Patients throughout Arizona who need assistance with a letter, form, or other physician documentation can learn more about our Medical Documentation Services or explore the Medical Documentation Resource Center.
Frequently Asked Questions
Can any physician write a letter of medical necessity?
A physician may be able to write a medical necessity letter when the requested opinion is within their professional scope and they have sufficient clinical information to support it. Certain requests may be more appropriately addressed by the clinician treating the condition or by a particular specialist.
Does a letter of medical necessity guarantee insurance approval?
No. A letter explains the physician's clinical rationale. The insurance company or other reviewing organization makes the final coverage or authorization decision according to its own requirements and the patient's plan.
Do I need an appointment for a medical necessity letter?
Sometimes. A new or complex request commonly requires an evaluation, particularly if the physician lacks current information about the relevant condition. A separate appointment may not always be necessary when the physician recently evaluated the condition and has adequate information in the medical record.
What if my insurance company already denied the treatment?
Provide the denial letter to your physician. It may identify the specific reason for the denial or the criteria that were not met. When medically appropriate, the physician may be able to provide additional documentation or an appeal addressing those issues.
Can a physician write exactly what I ask them to include?
A patient can explain what documentation has been requested and provide the organization's instructions, but the physician must determine independently what can be medically supported. A physician should not certify inaccurate, misleading, or unsupported information.
How long should a medical necessity letter be?
There is no required universal length. The letter should contain enough relevant information to explain the diagnosis, clinical circumstances, requested service, and medical reasoning without adding unnecessary information.
Clinical Review and Medical Sources
Medical necessity requirements vary among insurance plans and other reviewing organizations. This article is intended to explain the clinical factors physicians may consider rather than establish the coverage requirements of any particular insurer.
For authoritative information about Medicare coverage and medical documentation, readers can review the Centers for Medicare & Medicaid Services Medicare Coverage Determination Process and the CMS Documentation Matters Toolkit.
Physicians and medical practices navigating insurance authorization requirements can also review the American Medical Association's prior authorization resources.
Individual insurance plans may use different medical-necessity definitions, prior-authorization procedures, and coverage requirements. Patients should verify plan-specific requirements directly with their insurer.
Medical disclaimer: This article is provided for general educational purposes and does not constitute individualized medical, insurance, or legal advice. Medical necessity and insurance coverage decisions depend on the patient's individual circumstances and the requirements of the organization reviewing the request.
About the Author
YiQiu Hu, NMD is an Arizona-licensed naturopathic physician and concierge medicine provider at Ask Dr. Hu. His clinical approach emphasizes individualized medical evaluation, careful review of supporting evidence, clear patient communication, and accurate physician documentation.
Dr. Hu provides medical documentation services for Arizona patients when clinically appropriate, including medical necessity letters, employment and medical leave documentation, disability-related forms, work restrictions, medical clearances, and other physician-completed documentation.
Learn more about Dr. Hu and the Ask Dr. Hu medical team or visit Medical Documentation Services in Arizona.