How do I appeal a CARC 55 denial?

Primary argument: The denied treatment is not experimental or investigational under any recognized standard: it is FDA-approved or FDA-cleared for the indication being treated and is covered by Medicare contractors under published Local Coverage Determinations with defined clinical criteria the patient meets. The payer's contrary internal classification is an evidence question it must defend — and because medical-management standards that exclude benefits 'based on whether the treatment is experimental or investigative' are explicitly listed as non-quantitative treatment limitations under the MHPAEA regulations (45 CFR 146.136(c)(4)(ii)(A)), the plan may not apply that exclusion more stringently to behavioral-health treatments than to comparable medical/surgical treatments. Supporting points: Esketamine (Spravato) has been FDA-approved for treatment-resistant depression since March 5, 2019 (NDA 211243), and Medicare's own TMS coverage policy states that TMS 'is FDA approved for the treatment of depression' — a treatment used within its FDA-sanctioned indication cannot reasonably be labeled investigational. Medicare Local Coverage Determinations (e.g., L34998) cover TMS for adults with major depressive disorder after failure or intolerance of adequate psychopharmacologic treatment; the payer should be required to reconcile its experimental designation with published Medicare coverage standards and identify the specific evidence review it relied on. Under the MHPAEA regulations, the processes, strategies, and evidentiary standards used to apply an experimental/investigational exclusion to mental-health benefits must be comparable to, and applied no more stringently than, those used for medical/surgical benefits — we are entitled to the plan's written criteria for this classification. A denial that rests on a determination that a treatment is experimental or investigational is expressly one of the denial types eligible for independent external review, where the plan's internal policy is tested against the actual evidence by a reviewer the plan must obey.

What public sources support a CARC 55 appeal?

X12 — Claim Adjustment Reason Codes (official): Official wording of CARC 55 (start 01/01/1995, last modified 07/01/2017) (https://x12.org/codes/claim-adjustment-reason-codes) | eCFR — 45 CFR 146.136 (MHPAEA final rules): Illustrative NQTL list at (c)(4)(ii)(A) expressly includes medical management standards excluding benefits 'based on whether the treatment is experimental or investigative'; NQTLs may not be applied more stringently to MH/SUD than medical/surgical benefits (https://www.ecfr.gov/current/title-45/section-146.136) | FDA — Drugs@FDA, NDA 211243 (Spravato / esketamine): Official FDA approval record for Spravato (esketamine) nasal spray, original approval 03/05/2019 — establishes the drug is FDA-approved, not experimental (https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=211243) | CMS — Medicare Coverage Database, LCD L34998 (TMS for Major Depressive Disorder): Medicare contractor covers TMS for adults with MDD with defined criteria (failure/intolerance of adequate pharmacologic trials) and states TMS 'is FDA approved for the treatment of depression and obsessive-compulsive disorders' (https://www.cms.gov/medicare-coverage-database/view/lcd.aspx?LCDId=34998) | HealthCare.gov — External review of health plan decisions: Denials involving 'a determination that a treatment is experimental or investigational' are eligible for independent external review, and insurers are required by law to accept the external reviewer's decision (https://www.healthcare.gov/appeal-insurance-company-decision/external-review/)

CARC Code

CARC 55 Denial Appeal

Experimental / investigational treatment

Procedure/treatment/drug is deemed experimental/investigational by the payer.

Draft your CARC 55 appeal free →See all codes

Why CARC 55 hits behavioral-health claims

Behavioral health is where payer 'experimental' lists lag the evidence hardest. TMS (CPT 90867-90869) and esketamine (Spravato) are FDA-cleared/approved for treatment-resistant depression and covered by Medicare contractors under published LCDs, yet many commercial medical policies — which are updated slowly and reviewed against older literature — still tag them, along with newer protocols like theta-burst stimulation and intensive outpatient innovations, as experimental/investigational. The practical result: the small BH practices actually delivering guideline-supported interventions for treatment-resistant patients absorb CARC 55 denials that comparable-evidence medical/surgical treatments rarely face.

The winning argument

The denied treatment is not experimental or investigational under any recognized standard: it is FDA-approved or FDA-cleared for the indication being treated and is covered by Medicare contractors under published Local Coverage Determinations with defined clinical criteria the patient meets. The payer's contrary internal classification is an evidence question it must defend — and because medical-management standards that exclude benefits 'based on whether the treatment is experimental or investigative' are explicitly listed as non-quantitative treatment limitations under the MHPAEA regulations (45 CFR 146.136(c)(4)(ii)(A)), the plan may not apply that exclusion more stringently to behavioral-health treatments than to comparable medical/surgical treatments.

Esketamine (Spravato) has been FDA-approved for treatment-resistant depression since March 5, 2019 (NDA 211243), and Medicare's own TMS coverage policy states that TMS 'is FDA approved for the treatment of depression' — a treatment used within its FDA-sanctioned indication cannot reasonably be labeled investigational.
Medicare Local Coverage Determinations (e.g., L34998) cover TMS for adults with major depressive disorder after failure or intolerance of adequate psychopharmacologic treatment; the payer should be required to reconcile its experimental designation with published Medicare coverage standards and identify the specific evidence review it relied on.
Under the MHPAEA regulations, the processes, strategies, and evidentiary standards used to apply an experimental/investigational exclusion to mental-health benefits must be comparable to, and applied no more stringently than, those used for medical/surgical benefits — we are entitled to the plan's written criteria for this classification.
A denial that rests on a determination that a treatment is experimental or investigational is expressly one of the denial types eligible for independent external review, where the plan's internal policy is tested against the actual evidence by a reviewer the plan must obey.

Public sources you can cite

Every argument traces to a verified public source — no invented citations.

Sample appeal letter body

Replace the {{placeholders}} with your own information before sending.

We are appealing the denial of {{treatment_name}} for {{patient_reference}}, denied under CARC 55 as experimental/investigational. That designation cannot be reconciled with this treatment's regulatory and coverage status: it is {{fda_status}} for {{indicated_condition}}, and Medicare contractors reimburse it under published coverage policy ({{coverage_policy_reference}}) with defined clinical criteria this patient satisfies, as documented by {{prior_treatment_history}}. A treatment that is FDA-approved or FDA-cleared for the condition being treated and covered under published Medicare coverage policy is, by any reasonable evidentiary standard, neither experimental nor investigational. We further note that under the Mental Health Parity and Addiction Equity Act, medical-management standards that limit or exclude benefits based on whether a treatment is experimental or investigative are non-quantitative treatment limitations (45 C.F.R. § 146.136(c)(4)(ii)(A)) whose processes and evidentiary standards may not be applied more stringently to behavioral-health benefits than to medical/surgical benefits. We formally request the plan's specific written experimental/investigational criteria, the evidence review supporting this classification, and the qualifications of the reviewer who applied it. Because this denial rests on an experimental/investigational determination, it is eligible for independent external review, and we intend to pursue that review if the denial is not reversed.

You'll need to supply: patient_reference (member ID / claim # — fill locally), treatment_name (e.g., repetitive TMS, esketamine/Spravato), fda_status (e.g., "FDA-approved since March 5, 2019 (NDA 211243)" or "delivered via an FDA-cleared device"), indicated_condition (e.g., treatment-resistant major depressive disorder), coverage_policy_reference (e.g., Medicare LCD L34998, or the payer's own medical policy number), prior_treatment_history (e.g., two adequate-dose, adequate-duration antidepressant trials failed or not tolerated)

What this argument cannot ground

Honest gaps — no fabricated sources.

These arguments are strongest when the treatment is FDA-approved/cleared AND used within its labeled indication AND the patient meets published coverage criteria (e.g., LCD-style failed-trial requirements). Off-label or emerging uses — racemic IV ketamine for depression, accelerated/theta-burst schedules beyond cleared parameters, psilocybin-assisted therapy — genuinely lack the same regulatory grounding; for those, lean on peer-reviewed evidence and external review rather than the 'not experimental' framing.
If CARC 55 arrives with group code CO under a plan document that categorically excludes the specific service, the appeal must attack the classification itself (and parity comparability), not medical necessity; confirm the plan's exclusion language before drafting.
Medicare LCDs are cited as evidence of mainstream coverage standards; they are persuasive but not binding on commercial payers.
The MHPAEA NQTL argument ultimately requires showing the plan applies its experimental exclusion more stringently to BH than to med/surg — small practices rarely have visibility into the plan's comparative analysis, so frame it as a demand for the written criteria and comparability documentation.
External review rights as described on HealthCare.gov apply to non-grandfathered plans; grandfathered plans and some self-funded arrangements follow different review procedures.

Argument confidence85%

Draft your CARC 55 appeal in 60 seconds

Get a complete, citation-grounded appeal letter — free for your first 3 drafts.

Draft your CARC 55 appeal free →

No credit card required. De-identified by design — we never touch patient data.