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A prior authorization support letter is a narrative letter a treating clinician sends to a health plan to justify why a mental health service should be authorized before it is delivered, or continued. It states the diagnosis, symptoms, functional impairment, treatment history, and the exact service requested, mapped to the plan's medical-necessity criteria. Many plans do not require it for routine outpatient therapy.
Treating therapists, psychologists, counselors, social workers, prescribers
Health plan utilization reviewer, behavioral health managed care
400 to 700 words · 15 to 30 minutes by hand (clinical team estimate)
Payer-facing medical-necessity letter (compare: medical necessity letter, appeal letter)
Before a service that needs prior authorization, or to extend one (concurrent review)
A payer-driven letter, not a mandated form; content maps to the plan's medical-necessity criteria
A prior authorization support letter is the clinical narrative a treating clinician sends to a health plan to justify a mental health service before the plan will approve it. It belongs to the family of utilization-management and medical-necessity documentation. Clinicians and payers also call it a prior auth letter, a pre-authorization or precertification letter, or a letter supporting a prior authorization request. Prospective review happens before treatment starts; concurrent review happens while treatment is ongoing, to extend an existing authorization.
Two distinctions carry the whole document. First, the letter is not the request. The request is the administrative transaction a plan processes through its portal, its own form, or the standard electronic transaction that federal rules recognize; the support letter is the clinical evidence attached to that request, and a letter on its own may not count as a valid request. Second, prior authorization is not universal. Many plans do not require it for routine outpatient psychotherapy: in a 2025 review, none of nine Medicare Advantage organizations required prior authorization for routine in-network counseling or psychotherapy. Plans reserve it for psychological and neuropsychological testing, higher levels of care such as intensive outpatient or residential treatment, and plans that authorize therapy in blocks of sessions. No statute prescribes a letter format. What the plan requires is medical-necessity content mapped to its own criteria, which makes this a letter of medical necessity written for a utilization reviewer, distinct from an appeal letter that a clinician writes after a denial.
Therapists, psychologists, counselors, clinical social workers, and prescribers write these letters when a plan requires authorization before it will cover a service. That is most common for psychological and neuropsychological testing, applied behavior analysis, transcranial magnetic stimulation, and admissions to higher levels of care, and for Medicaid managed care and behavioral-health carve-out plans that authorize outpatient therapy in blocks and require a clinical update to extend. A support letter beats a bare form when the request needs a clinical story: a partial treatment response, a level-of-care decision, or an out-of-network single-case agreement. When the plan has already denied the service, the task shifts to an appeal letter instead.
Header and recipient. Your practice identifiers and the plan's utilization-management or behavioral-health prior-authorization unit, with the fax or portal reference. Pitfall: sending it to general claims instead of the utilization-management address, so it never reaches a reviewer.
Member and request identifiers. Member name, date of birth, member or policy ID, group number, the exact code and units or dates requested, and the prior authorization number for a continuation. Pitfall: omitting the member ID or the exact code and units, which stalls the request at intake.
Diagnosis. The ICD-10 code or codes that support the requested service. Pitfall: treating the diagnosis code as the justification; the code anchors the request, the impairment justifies it.
Clinical presentation and severity. Current symptoms with a dated, validated measure such as the PHQ-9, GAD-7, or PCL-5, and the course over time. Pitfall: adjectives without measures; a dated score carries more weight with a reviewer than the word "severe".
Functional impairment. The concrete effect on work, school, relationships, self-care, and safety. Pitfall: leaving impairment out; medical necessity turns on function, not symptoms alone.
Treatment history and response. What has been tried, the response so far, and why a lower level of care is insufficient. Pitfall: no treatment history, so the reviewer cannot see why the requested service is the right next step.
Requested service and medical-necessity justification. The exact service, frequency, and duration or level of care, mapped to the plan's criteria, with the clinical risk if it is not authorized. Pitfall: an open-ended request; name the units and the dates so the reviewer can approve a defined span.
Closing, peer-to-peer offer, and signature. Offer a peer-to-peer discussion, then sign with credentials, license number, and NPI, and add a supervisor co-signature where required. Pitfall: no signature block, or a missing supervisor co-signature for a pre-licensed author.
[Practice letterhead: name, credentials, license #, NPI, address, phone, fax]
[Date]
[Health plan / behavioral health managed care organization]
[Utilization Management / Prior Authorization Department]
RE: Prior authorization request ( ) initial ( ) continued
Member: [name] Date of birth: [ / / ]
Member/policy ID: [ ] Group #: [ ]
Requested service/code: [CPT/HCPCS] Units/frequency/dates: [ ]
Prior authorization # (continuation): [ ]
Dear Utilization Reviewer,
I am the treating [discipline] for the member above and am requesting prior
authorization for the service described below.
Diagnosis: [ICD-10 code(s) and description]
Clinical presentation and severity: [current symptoms; validated measure
scores with dates, such as PHQ-9, GAD-7, PCL-5; onset and course]
Functional impairment: [effect on work, school, relationships, self-care, safety]
Treatment history and response: [prior and current treatment, medications,
response, why a lower level of care is insufficient]
Requested service and medical necessity: [exact service, frequency, and
duration or level of care, mapped to the plan's criteria (MCG, InterQual,
ASAM, LOCUS), and the clinical risk if it is not authorized]
I am available for a peer-to-peer discussion. Please contact me at [phone].
Sincerely,
[Signature]
[Name, credentials, license #, NPI]
[Supervisor name and credentials, if required]Free to use and share, no signup. The PDF includes a one-page cheat sheet with section-by-section pitfalls and a pre-send checklist; the DOCX is the blank template, ready to adapt.
Scenario: an adult member in outpatient therapy under a Medicaid managed care plan that authorizes psychotherapy in blocks and requires a clinical update to extend. Recurrent major depression with generalized anxiety. All details are fictional.
From: J. Okafor, LCSW, NPI 1000000000, Riverside Counseling Associates, Fort Collins, CO · Date: July 15, 2026 · To: Mountain State Health Plan, Behavioral Health Utilization Management
RE: Prior authorization, continued outpatient psychotherapy. Member: A.R. · DOB: 03/1988 · Member ID: MSHP000000000 · Requested: 12 sessions of 90837, weekly, 08/01/2026 to 10/31/2026 · Prior authorization #2026-000123 (10 sessions authorized 05/01 to 07/31/2026)
Dear Utilization Reviewer,
I am the treating clinician for the member above and am requesting authorization to continue weekly individual psychotherapy for a further 12 sessions. This letter sets out the clinical basis for continued treatment.
Diagnosis: Major depressive disorder, recurrent, moderate (F33.1); generalized anxiety disorder (F41.1).
Clinical presentation and severity: Treatment began 05/06/2026 with moderate to severe symptoms (PHQ-9 18, GAD-7 15). After 10 sessions of cognitive behavioral therapy, symptoms have improved but remain moderate (PHQ-9 12, GAD-7 11 on 07/08/2026). The member reports low mood most days, initial insomnia, and anticipatory worry about returning to full-time work.
Functional impairment: The member is on a graduated return-to-work plan and cannot yet sustain full hours because of concentration difficulty and fatigue. Anxiety continues to limit driving and contact outside the home.
Treatment history and response: The primary care physician started sertraline in April 2026, continued at a stable dose. Psychotherapy has produced a measurable but partial response; the member now uses cognitive restructuring with less coaching. The gains are consistent with continued treatment, and ending now carries a substantial relapse risk given the recurrent course.
Requested service and medical necessity: I am requesting 12 additional weekly sessions of individual psychotherapy (90837) over the next authorization period, to consolidate partial gains, complete the return to work, and prevent relapse. The requested frequency and duration are consistent with the plan's outpatient behavioral-health medical-necessity criteria. I am available for a peer-to-peer review.
Sincerely,
J. Okafor, LCSW · License 000000 · NPI 1000000000
This sample is fictional and for educational purposes. It does not describe a real patient.
Writing these after every session? BastionGPT drafts complete notes from bullets, dictation, or a transcript.
Generate a note from bulletsThe letter itself is a convention; what a plan enforces is medical-necessity content mapped to its own criteria. Behavioral-health plans commonly measure requests against a named framework: MCG or InterQual for general medical necessity, the ASAM Criteria for substance-use levels of care, and LOCUS or CALOCUS for psychiatric level-of-care decisions. Name the framework the plan actually uses rather than a generic reference, and show, point by point, how the member meets it. Mental health parity sits behind all of this. Since 2021, federal law has required health plans to perform and document a comparative analysis showing that any nonquantitative treatment limitation, and prior authorization is a classic one, is applied no more stringently to mental health and substance-use benefits than to comparable medical and surgical benefits. A clinician does not include that analysis in a routine letter, but it is worth requesting when a denial looks like a more stringent behavioral-health standard.
Two practical points close the loop. First, plans owe a decision on a clock. For employer plans governed by ERISA, the federal claims-procedure rule sets the outer limits: 72 hours for an urgent request, 15 days for a standard pre-service request, and 30 days after service (LAW, 29 CFR 2560.503-1). Federal reform shortens standard decisions to 7 calendar days and urgent decisions to 72 hours for Medicare Advantage, Medicaid, and CHIP starting in 2026, though it does not cover drugs (LAW, CMS-0057-F), and states set their own rules: Minnesota now bars prior authorization for outpatient mental health and substance-use treatment other than medication. One caveat worth knowing: many state prior-authorization reforms do not reach self-funded employer plans, which ERISA governs. Second, an authorization is a coverage decision, not a promise of payment; it remains subject to eligibility, benefit limits, and correct billing. In Medicare Advantage, an approved authorization is binding on the plan, which may not later deny the service for lack of medical necessity except for good cause (LAW, 42 CFR 422.138). Keep the letter in the record; it becomes the backbone of an appeal if the request is denied. See also the letter of medical necessity for coverage requests that are not tied to a prior authorization.
The pattern behind most denials is a request that does not connect the service to documented medical necessity. Federal oversight shows how often the process itself errs: an HHS Office of Inspector General review found that 13 percent of the prior-authorization requests Medicare Advantage plans denied actually met Medicare coverage rules (OIG, 2022). The denials are rarely tested: an analysis of 2024 data found that only 11.5 percent of denied Medicare Advantage prior-authorization requests were appealed, yet 80.7 percent of those appeals were overturned (KFF, 2024). A clear letter is what prevents the denial in the first place. The BastionGPT Clinical Advisory Board sees the same errors most often in prior authorization letter reviews:
| Aspect | United States | Canada | Australia |
|---|---|---|---|
| Status | Set by each plan (PAYER POLICY); federal law regulates the process, not a letter format. Parity law, ERISA timeframes, and the 2026 CMS reform apply; some states, such as Minnesota, now bar prior authorization for outpatient mental health | Prior authorization generally does not apply to publicly funded psychology; provincial drug plans use special-authority approval, and a federal benefit (NIHB) requires prior approval for mental-health counselling beyond an initial allowance | MBS Better Access sessions are not prior-authorized; a mental health treatment plan is a care-planning record, not insurer approval. PBS Authority Required medicines and NDIS supports do need prior approval |
| Terminology | Prior authorization, pre-authorization, precertification, pre-cert, prospective and concurrent review | Predetermination, special authority, exceptional access, exception drug status | Authority required, prior approval, NDIS plan approval |
| What changes | Whether a service needs authorization at all, the plan's criteria framework, and whether the plan is fully insured or self-funded | The public system rarely covers private therapy, so the letter usually supports a private insurer or a drug plan | The referral and mental health treatment plan drive access; there is no session-level pre-authorization for therapy |
| Retention | No universal federal chart-retention rule; state law and payer contracts govern | Provincial college standards; Ontario expects about 10 years from the last interaction | State rules; New South Wales requires 7 years for adults and until age 25 for minors |
The letter travels across all three countries. What changes is whether authorization applies at all, and to which service, so adapt the request to the plan or program you are writing to.
BastionGPT is specifically trained, tuned, and clinically tested on prior authorization support letters.
See how clinicians use it day to day on the AI therapy notes page.
Many BastionGPT users report saving more than 90 minutes per day on documentation.
HIPAA-compliant with a signed BAA on every plan. Your data is never used to train models. BastionGPT drafts, you review and sign.
No, not inherently. Many plans cover routine outpatient psychotherapy without prior authorization: in a 2025 review, none of nine Medicare Advantage organizations required it for routine in-network counseling or psychotherapy, and some states, including Minnesota, now bar it for outpatient mental health. Prior authorization is more common for testing, higher levels of care, and plans that authorize therapy in blocks. Always check the member's plan before writing.
A prior authorization support letter backs a specific authorization request against a plan's criteria, before or during the service. A letter of medical necessity is the broader genre: it explains why a service, drug, device, or exception is medically necessary and can be used inside a prior authorization, a benefit exception, or an appeal. The title alone does not start a prior authorization.
No. A support letter is proactive: it justifies a service before it is delivered, or to extend one. An appeal letter comes after an adverse determination, invokes the plan's review rights, and answers the specific reason the plan gave for the denial. Keep your support letter; it becomes the foundation of the appeal if the request is denied.
The treating clinician supplies or authenticates the clinical rationale, because that is the part a reviewer relies on. Billing staff often transmit the request, but they should not attest to clinical facts. A prescriber handles medication-specific requests, and a pre-licensed clinician's supervisor co-signs where the payer or the professional rules require it.
It depends on the plan type. For employer plans governed by ERISA, the outer limits are 72 hours for an urgent request, 15 days for a standard pre-service request, and 30 days after service. Starting in 2026, Medicare Advantage, Medicaid, and CHIP must decide standard requests within 7 calendar days and urgent requests within 72 hours, though that reform does not cover drugs. Many states set shorter deadlines of their own.
Not by itself. An authorization confirms the plan approved the service on the information it had; payment still depends on eligibility on the service date, benefit limits, network status, correct coding, and timely filing. Medicare Advantage is stronger: once a service is approved, the plan generally may not later deny it for lack of medical necessity except for good cause.
Submit a concurrent-review letter before the current authorization ends, documenting remaining symptoms, progress, why step-down is premature, current risk, and the requested dates and units. Do not assume the plan will backdate coverage. Under ERISA, ending an approved course early is itself an adverse determination, and in Medicare Advantage an approved course stays valid as long as it is medically necessary.
Yes. Federal parity law treats prior authorization as a nonquantitative treatment limitation, and since 2021 plans must document that they do not apply it more stringently to mental health and substance-use benefits than to comparable medical and surgical benefits. If a behavioral-health denial looks more restrictive than the medical side, you can request the plan's comparative analysis and the exact criteria it used.
Yes. Give it the diagnosis, a few measure scores, the functional impairment, the treatment history, and the service you are requesting, and it drafts a letter you can review and adapt to the plan's criteria. BastionGPT is HIPAA-compliant with a signed BAA on every plan, and your data is never used to train models.
The compliance claims on this page trace to these authorities, last verified July 2026:
Educational content, not legal or billing advice. Sample notes are fictional. Follow your organization's policies and your board, payer, and jurisdiction requirements.