How to appeal a denied claim for medical-necessity / coding.
When a plan denies coverage on a medical-necessity or coding rationale — “medical necessity not established,” “clinical criteria not met,” “experimental / investigational,” or a coding-bundle mismatch — the appeal letter is built around the patient-specific clinical counterweight to the carrier’s criteria-based framework, not the underlying diagnosis. Carriers adjudicate medical-necessity against three standard frameworks — MCG (formerly Milliman Care Guidelines), InterQual (Change Healthcare), and the carrier’s own internal clinical criteria — and the dispute is whether those criteria were properly applied to this patient’s specific clinical scenario. The governing framework varies by plan type: the ACA internal-claims-process obligation at 42 U.S.C. § 300gg-19a (implementing at 45 C.F.R. § 147.136) governs the appeal channel for ACA marketplace plans, the ERISA § 503 claims-procedure rule at 29 C.F.R. § 2560.503-1 governs the internal-appeal process for self-funded ERISA plans — with the patient-specific clinical letter as the strongest single counterweight — and the per-state adverse-determination statute applies to fully-insured plans.
01 · What a medical-necessity denial looks like on the EOB
A medical-necessity / coding denial — and the patient-specific counterweight framework that defeats it.
Medical-necessity is a contractual and regulatory standard, not a clinical opinion — the plan’s determination letter and EOB will cite a reason code such as “medical necessity not established,” “not medically necessary,” “clinical criteria not met,” “level of care not appropriate,” or for coding denials, “procedure code does not match diagnosis” / “bundled services — separate procedure not supported.” The dispute is not whether the prescribed service is clinically indicated in the abstract; it is whether the patient-specific factor pattern on the chart defeats the criteria-based screen the carrier applied. Coding denials are a sibling category where the plan’s review has flagged a CPT/ICD mismatch — typically the diagnosis code does not support the procedure code under the carrier’s coding manual, or two services that were billed separately should have been bundled.
Carriers adjudicate medical-necessity against three standard frameworks — MCG (formerly Milliman Care Guidelines, the dominant commercial criteria set used by UnitedHealthcare, Aetna, Cigna, and most Blues plans), InterQual (Change Healthcare, the dominant criteria set used by Centene subsidiaries, many state Medicaid plans, and several regional carriers), and the carrier’s own internal clinical criteria (typically a proprietary Medical Policy or Coverage Policy document that the carrier will only release to the enrollee on appeal). The criteria screens out patient-specific factors the prescriber weighs clinically — comorbidities, prior treatment response, age-of-onset, pregnancy, documented contraindication, severity grading — and treats each request against a population-level threshold. The counterweight on the appeal is the treating physician’s letter that names the patient-specific factor pattern the criteria screen out, plus the prescribing physician’s clinical expertise as required by ERISA § 503 at 29 C.F.R. § 2560.503-1.
A well-built medical-necessity appeal letter substitutes a patient-specific clinical rationale for the carrier’s criteria-based denial. The three named counter-arguments — patient-specific clinical factors the criteria screen out, clinical-criteria mismatch (the cited guideline does not address the patient’s clinical scenario, or the carrier has used a non-public / proprietary guideline), and the treating physician’s letter as the strongest single counterweight — each give the prescriber a clinically specific basis to bypass a wrong-screen denial. Each is anchored in a different corner of the clinical record: a documented comorbidity ladder, a guideline-versioning audit, a treating-physician clinical letter naming the patient-specific factors with citation to medical literature. The letter branches on whether the request is filed pre- (expedited, urgent) or post-denial (the EOB cites the reason code, the appeal reverses the denial). The right framework on the federal side is the ACA internal-claims-process rule at 42 U.S.C. § 300gg-19a (implementing at 45 C.F.R. § 147.136), the ERISA claims-procedure rule at 29 C.F.R. § 2560.503-1, or the per-state adverse-determination statute in the controlling jurisdiction.
01 · The three counter-arguments
The patient-specific counterweight framework — three named grounds the letter must build on.
01
Patient-specific clinical factors the criteria screen out
The patient has a documented clinical factor pattern that the carrier’s MCG / InterQual / internal screen does not accommodate — a comorbidity the criteria model treats as an exclusion threshold, a prior treatment response profile (the patient has already failed the preferred step with documented labs / imaging / patient-reported outcomes), an age-of-onset characteristic the criteria oversimplify, a pregnancy or perinatal factor the criteria exclude from the standard branch, or a documented contraindication to the preferred-step agent that the carrier has ignored. The supporting documentation is the chart’s comorbidity ladder, the labs / imaging / patient-reported outcomes drawn during the prior trial, the allergy / contraindication notation, and the prescriber’s contemporaneous assessment of why the criteria screen out this case. This is the most common counter-argument because the factor pattern usually exists on the chart — the documentation just needs to be surfaced against the criteria the carrier applied.
02
Clinical-criteria mismatch
The carrier’s denial letter cites a clinical-criteria document — an MCG guideline, an InterQual subset, or the carrier’s internal coverage policy — that does not address the patient’s clinical scenario, is outdated, or is non-public / proprietary. The appeal surfaces the criteria-versioning issue (the cited guideline is missing the patient’s factor pattern), the patient-scenario-coverage issue (the cited guideline addresses a different patient population), or — under ERISA § 503 — the carrier’s failure to disclose the criteria document on which the denial was based. The supporting documentation is the published MCG / InterQual version available in the public reference, the carrier’s published coverage policy (when one exists), the chart entries that demonstrate the patient falls outside the cited guideline, and a prescriber letter documenting that the clinical factors exceed the cited criteria’s applicability range. When the carrier has used a non-public / proprietary clinical review without disclosing the medical experts consulted — the disclosure required at 29 C.F.R. § 2560.503-1(j)(4) — the letter frames this as a procedural-defect reversal rather than a clinical re-argument.
03
Treating physician’s letter — the strongest counterweight
The treating physician’s clinical letter is the strongest single counterweight on a medical-necessity denial because ERISA § 503 at 29 U.S.C. § 1133 requires the plan to give the claim a “full and fair review,” and the implementing language at 29 C.F.R. § 2560.503-1(b)(1) prohibits denials that are arbitrary in light of the treating physician’s clinical judgment. The letter must name: (i) the patient’s diagnosis with the supporting chart entries, (ii) the prescribed treatment (drug, dose, duration, modality) with the prescribing rationale, (iii) the carrier’s criteria-based denial rationale with the specific guideline or policy cited on the EOB, (iv) the patient-specific clinical factor pattern that defeats the criteria screen — comorbidities, prior response, age-of-onset, contraindication, severity grading — with chart-citation support, (v) the medical literature that supports the prescribed treatment over the carrier-preferred alternative, and (vi) any prior trial on the carrier-preferred agent with the documentation of inadequate response or adverse event. The supporting documentation is the prescriber’s letter on the practice letterhead, the chart entries referenced in the letter, the published clinical guidelines where applicable, and any peer-reviewed literature that supports the prescribed treatment over the carrier’s preferred alternative.
01 · State-specific medical-necessity levers
Three jurisdictions with a medical-necessity-specific lever on the EOB.
01
Illinois · MacCutcheon mental-health medical-necessity standard
IL MacCutcheon
Illinois fully-insured plans are bound by 215 ILCS 134/25, the Mental Health and Substance Use Disorder Treatment Parity Act, which adopts the federal Stephen M. MacCutcheon parity standard — the plan’s medical-necessity criteria for mental-health and substance-use-disorder treatment cannot be more restrictive than the criteria applied to medical/surgical treatment. The appeal cites the parity standard directly, attaches the treating physician’s clinical letter demonstrating the medical-necessity criteria the plan would apply to an equivalent medical/surgical case, and frames the denial as a parity violation rather than a clinical dispute. Mental-health medical-necessity denials under Illinois law typically clear the bar under 215 ILCS 134/25 when the prescribed treatment is the standard-of-care for the diagnosis and the plan has applied a more restrictive criteria set than it applies to a comparable medical/surgical case.
02
California · Knox-Keene § 1367.01 DMHC medical-necessity framework
CA DMHC MN
California Knox-Keene licensees (Kaiser Permanente, Health Net, Blue Shield of California, Anthem Blue Cross CA products) are bound by Cal. Health & Safety Code § 1367.01 on the medical-necessity framework — Knox-Keene plans must use evidence-based clinical criteria and apply them consistently to enrollees with the same clinical profile. The DMHC Help Center (1-888-466-2219, www.dmhc.ca.gov) accepts complaints about medical-necessity denials, and Independent Medical Review (IMR) under § 1370.4 within 180 days of the final internal denial is the binding backstop — when the IRO physician reviewer overturns a medical-necessity denial, the carrier must comply within 3 business days. The appeal cites § 1367.01 directly, attaches the IMR application, and frames the dispute as a clinical-criteria-consistency dispute.
03
New York · Insurance Law § 4903 medical-necessity dispute + § 4914 external appeal
NY Med-Nec
New York fully-insured plans are bound by N.Y. Ins. Law § 4903 on medical-necessity disputes, with the controlling state external appeal channel at N.Y. Ins. Law § 4914 — when the plan’s denial is based on medical-necessity, the enrollee has four months from the final internal denial to file an external appeal with the NY Department of Financial Services, and the external appeal decision is binding on the carrier. The appeal cites § 4903 on the medical-necessity framework, attaches the treating physician’s clinical letter referencing the carrier’s failure to engage with the patient-specific factor pattern, and routes the dispute to § 4914 external appeal if the carrier refuses to reverse on internal review. Urgency framing applies under the same four-month window with expedited external appeal available for ongoing treatment.
01 · ERISA procedural note
For self-funded ERISA plans — arbitrary-denial standard at 29 C.F.R. § 2560.503-1 plus ACA internal-claims rights at 42 U.S.C. § 300gg-19a.
Self-funded ERISA plans — typically larger employer group plans where the employer pays the claims rather than buying insurance from a carrier — run through the Department of Labor’s claims-procedure rule at 29 C.F.R. § 2560.503-1, implementing ERISA § 503 at 29 U.S.C. § 1133. The regulation requires the plan to give the claim a “full and fair review,” and the implementing language at § 2560.503-1(b)(1) prohibits denials that are arbitrary. Specifically, the clinical-reviewer disclosure at (j)(4) requires the plan to identify the medical or vocational experts whose advice the plan relied on — and the carrier’s failure to identify the criteria document the reviewer consulted, or the version of MCG / InterQual the reviewer applied, is the procedural lever for a denial that does not survive the arbitrary-denial standard. The member is entitled to the claims file under (m) without charge to surface the criteria document, the reviewer’s notes, and any inconsistent application of the criteria to comparable cases. ACA marketplace plans bound by 42 U.S.C. § 300gg-19a (implementing at 45 C.F.R. § 147.136) attach an analogous internal-claims-process channel with the Independent Review Organization (IRO) binding-channel under § 147.136(d).
The arbitrary-denial standard is the lever that distinguishes a denied claim from a denial the plan must defend. Specifically, the plan must show (i) that the medical-necessity criteria it applied are written into the plan document (or were disclosed on request under the SPD requirement), (ii) that the criteria-versioning the reviewer applied matches the published guideline the plan claimed to use, (iii) that the patient-specific clinical factors were considered and addressed in the denial letter, and (iv) that the clinical reasoning is on the record and authored by the named clinical experts under (j)(4). When any of those four are missing, the § 2560.503-1(b)(1) standard is not met, and the appeal letter frames the ask as a procedural-defect reversal under the federal claims-procedure rule — not as a re-litigation of the underlying medical-necessity determination. The ACA marketplace internal-claims channel at 45 C.F.R. § 147.136(b)(2)/(c) / (d) layers the IRO right on top: when the plan maintains the denial, the IRO is binding on the carrier, and the four-month external-review window runs from each new internal denial.
01 · Worked sample paragraph
A first-person appeal paragraph that has already survived one round.
Below is a worked survivor-language paragraph — the kind of letter a member writes after a medical-necessity denial has been re-denied on the same carrier-criteria rationale. The voice is first-person, the evidence is attached, and the citations frame the request as a procedural-defect reversal and a patient-specific clinical-counterweight, rather than a re-argument of the underlying diagnosis. The sample subject is a denied MRI after a course of conservative care failed on a less-expensive modality — a medical-necessity denial that turns on the imaging modality the prescriber selected, where the carrier applied the MCG imaging guideline to deny the MRI without engaging the patient-specific factors on the chart.
Re: Second-stage internal appeal — medical-necessity denial for [MODALITY], EOB dated [DATE]
I am writing as the patient and as the party who has previously filed a first-stage appeal of this denial. The plan’s determination dated [DATE] cited “medical necessity not established” for [MODALITY] and the carrier’s internal Coverage Policy [POLICY ID]; the treating physician’s clinical exception request was supported by the patient-specific clinical factor pattern on the chart — documented failure of the conservative-care modality [MODALITY A] over [WEEKS], a chart-recorded comorbidity [COMORBIDITY ICD] that the carrier’s MCG imaging guideline screens out, and the treating physician’s clinical letter dated [DATE] naming the patient-specific factors with citation to medical literature. The first-stage appeal was denied without identifying the medical or vocational experts whose advice the plan relied on — the disclosure required at 29 C.F.R. § 2560.503-1(j)(4) — without naming the MCG guideline version the reviewer applied, and without engaging the patient-specific factor pattern the treating physician submitted.
I am submitting additional clinical evidence to satisfy the full and fair review required under ERISA § 503 at 29 C.F.R. § 2560.503-1(b)(1). Specifically: (1) the treating physician’s clinical letter documenting the patient-specific clinical factor pattern that defeats the cited MCG imaging guideline, dated [DATE]; (2) the chart entries recording the documented failure of [MODALITY A] over [WEEKS], with the imaging/labs/patient-reported outcomes drawn during the trial; (3) the medical literature — [CITATION, JOURNAL, YEAR] — that supports [MODALITY] over the carrier’s preferred [MODALITY A] in patients with the patient’s comorbidity profile; and (4) the carrier’s claim file, requested under 29 C.F.R. § 2560.503-1(m), to surface the criteria document and the reviewer notes the plan considered. The ACA marketplace internal-claims-process obligation at 42 U.S.C. § 300gg-19a, implementing at 45 C.F.R. § 147.136, applies the same full-and-fair-review standard — and the parallel IRO right at 45 C.F.R. § 147.136(d) is binding on the plan once internal review is exhausted.
I am requesting a reversal of the medical-necessity denial, a determination that names the medical or vocational experts under (j)(4), disclosure of the full claims file under (m), and a written application of the cited MCG imaging guideline to the patient-specific clinical factor pattern on the chart. If the plan maintains the denial, I am preserving the IRO right at 45 C.F.R. § 147.136(d) (where applicable), the state external-review channel in my jurisdiction — N.Y. Ins. Law § 4914 (NY), Cal. Health & Safety Code § 1370.4 (CA), 215 ILCS 134/25 parity framework (IL), or the controlling state in another jurisdiction — and the civil action under ERISA § 502(a) at 29 U.S.C. § 1132(a)(1)(B) after exhaustion.
Cited: 42 U.S.C. § 300gg-19a; 45 C.F.R. § 147.136; 29 C.F.R. § 2560.503-1(b), (j)(4), (m); 29 U.S.C. §§ 1133, 1132(a)(1)(B).
Identifiers, member IDs, claim numbers, modality names, ICD codes, and street addresses in the sample paragraph above are placeholders — every name is invented, and only the controlling statute / CFR / USC citations are real (those are public law).
02 · Frequently asked
The ERISA, ACA, and state frameworks that apply on a medical-necessity or coding denial.
Cited: 45 C.F.R. § 147.136 internal claims · 42 U.S.C. § 300gg-19a ACA claims process · 29 C.F.R. § 2560.503-1 ERISA procedure
Browse by state
Pick your state to see the appeal framework that applies.
Every state has a different agency, timeline, and binding external-review channel — start with yours.
03 · Submit the medical-necessity / coding denial
The same denial, reversed with the patient-specific clinical letter.
Upload the EOB or denial letter, answer the four short intake questions, and Denvow picks the ACA internal-claims-process framework under 42 U.S.C. § 300gg-19a / 45 C.F.R. § 147.136 or the ERISA § 503 procedure under 29 C.F.R. § 2560.503-1 — and the letter branches on whether you’re at the first-stage internal appeal or the second-stage external review, with the treating physician’s letter as the strongest single counterweight.
Already in the intake? Pre-selected to “medical-necessity” as the Segment-Denial-Reason — answer the rest and submit.
Other denial-reason pages
Denvow is template-and-tooling, not legal counsel. For denials that genuinely need litigation, an ERISA fiduciary complaint, or a state-court remedy, we recommend a licensed attorney in the relevant jurisdiction — and will say so when we see one.