Understanding CARC 50 and CARC 96

Both CARC 50 and CARC 96 indicate that the payer has determined the billed service is not medically necessary. While they are closely related, there is a distinction:

  • CARC 50 (Non-covered services): The payer has determined that the entire service is not deemed medically necessary based on their coverage criteria. This applies to the service as a whole.
  • CARC 96 (Non-covered charges): The payer has determined that specific charges within the service are not medically necessary. This may apply to individual line items rather than the entire claim.

CARC 50 is the sixth most frequent reason for Medicare claim denials. When combined with CARC 96, medical necessity denials represent a significant portion of total denials across all payers — and they carry higher average denial amounts because they often involve specialized procedures and treatments.

Critical: CARC 50/96 Cannot Be Resubmitted — You Must Appeal

Unlike administrative denials (CARC 16, 18), medical necessity denials cannot be corrected and resubmitted. They must be sent to redetermination (formal appeal). If you do not file the appeal within 120 days of the denial date, you will miss the timely filing deadline permanently.

Why Medical Necessity Denials Are Different

Medical necessity denials are fundamentally different from administrative denials because they challenge the clinical judgment of the treating provider. The payer is not saying the claim data is wrong — they are saying the service should not have been performed, or that a less intensive alternative would have been sufficient.

This makes medical necessity denials harder to overturn, but the data shows they are still highly winnable when the right strategies are applied:

78%
Overturn rate for medical necessity denials when peer-to-peer reviews are requested — compared to 67% for written-only appeals.
Source: Aetna claims data analysis; Counterforce Health, 2025

The Peer-to-Peer Review: Your Most Powerful Tool

A peer-to-peer review is a direct phone conversation between the treating physician and a medical reviewer (typically a physician) at the insurance company. This is widely recognized as the single most effective strategy for overturning medical necessity denials.

How Peer-to-Peer Reviews Work

  • Timing: Typically scheduled within 5–10 business days after the request is made. Some payers require requests within 72, 48, or even 24 hours of the denial.
  • Duration: Usually 5–10 minutes.
  • Who participates: The treating physician and a medical reviewer from the same specialty at the payer.
  • Effectiveness: 78% overturn rate (compared to 67% for written-only appeals).
Request Early — Before the Written Appeal

Some payers do not allow peer-to-peer reviews after a formal written appeal has been filed. Always request the peer-to-peer review first, then follow up with the written appeal if needed. About half of U.S. states have laws requiring payers to make physicians available for peer-to-peer discussions.

Preparing for a Successful Peer-to-Peer

  1. Review the payer's clinical criteria. Know the specific policy or guideline the reviewer will be evaluating against. If the payer uses InterQual or Milliman Care Guidelines, obtain the relevant criteria in advance.
  2. Prepare a concise clinical summary. Present the patient's condition, functional status, treatment history, and why the specific service was medically necessary — all in 3–5 minutes.
  3. Document objective data. Peer reviewers respond to objective clinical data: vital signs, lab results, imaging findings, validated assessment scores, and functional measurements.
  4. Reference published guidelines. Cite evidence-based clinical guidelines, NCDs/LCDs, or specialty society recommendations that support the treatment.
  5. Be professional and focused. The reviewer is a colleague. Present your case clearly and factually. Avoid emotional arguments.

Specialty-Specific Strategies

Mental Health: Leveraging Parity Law

Mental health claim denials occur at rates 85% higher than medical claims, despite federal parity laws that mandate equal coverage. The Mental Health Parity and Addiction Equality Act (MHPAEA) of 2008, as amended in 2013, makes it illegal for insurers to apply more restrictive coverage criteria to mental health and substance use disorder services than to comparable medical/surgical services.

This is a critical tool for appeals. Data shows that appeals documenting specific parity violations achieve success rates approximately 3.2 times higher than those focusing solely on medical necessity.

Strategy for Mental Health Practices:

  • Document the specific parity violation in your appeal letter (e.g., "Medical inpatient admissions are authorized for 14 days; psychiatric admissions are limited to 5 days — this is a quantitative treatment limitation under MHPAEA").
  • Include detailed provider advocacy letters — appeals with detailed provider letters achieve approval rates of 64% compared to 29% for those with minimal documentation.
  • Document symptom severity and functional impairment using validated tools (PHQ-9, GAD-7, Columbia Suicide Severity Rating Scale). Comprehensive clinical documentation increases success rates 2.7 times compared to limited documentation.

Physical Therapy: Clinical Practice Guidelines

PT practices face high rates of medical necessity denials, particularly for extended treatment programs and specialized modalities. There is a significant lack of consensus on the definition of medical necessity across payers — a 2024 analysis found different criteria across 42 major medical insurance companies.

Strategy for PT Practices:

  • Cite specific Clinical Practice Guidelines (CPGs) in your appeal letter. Appeals citing CPG criteria achieve an 82% overturn rate compared to 58% for generic appeals.
  • Include objective outcome measures at every visit: range of motion, strength testing, functional capacity evaluations, and validated patient-reported outcome measures.
  • Document the specific functional limitation and how continued treatment addresses it — payers look for ongoing measurable progress toward defined goals.

Substance Abuse Treatment

Substance use disorder treatment is protected under both the MHPAEA and the Affordable Care Act's essential health benefits requirements. Despite these protections, substance abuse treatment denials remain common and are often not based on evidence-based criteria.

Strategy for Substance Abuse Treatment Providers:

  • Reference the ASAM (American Society of Addiction Medicine) Criteria for level of care placement. Most payers recognize ASAM as the standard for determining appropriate treatment intensity.
  • Document parity violations when residential treatment, PHP, or IOP receives more restrictive authorization windows than comparable medical admissions.
  • Include relapse history, withdrawal risk assessment, and co-occurring disorder documentation to support the prescribed level of care.

Cardiology: Evidence-Based Protocols

Cardiology practices face denial rates of 15–20% — significantly higher than the industry average. When clinical documentation lacks symptom duration, prior treatments, or clinical rationale, denials under CARC 50 or 96 are "almost guaranteed."

Strategy for Cardiology Practices:

  • Reference ACC/AHA (American College of Cardiology/American Heart Association) guidelines and appropriate use criteria in all appeals.
  • Document symptom severity, functional class, prior treatment failures, and risk stratification scores.
  • For advanced imaging (cardiac MRI, PET, CT angiography), document why the specific modality was chosen over lower-cost alternatives.

Clinical Documentation Improvement (CDI): Preventing Medical Necessity Denials

The most effective defense against medical necessity denials is clinical documentation that clearly supports the need for service before the claim is ever submitted. Clinical Documentation Improvement (CDI) programs focus on ensuring that provider documentation captures the clinical reasoning, severity, and specificity needed to withstand payer scrutiny.

CDI Best Practices

  1. Document the "why" at every encounter. Clinical notes should explicitly state why the specific service, medication, or procedure was necessary for this patient at this time — not just what was done.
  2. Use validated severity scales. Standardized assessment tools (PHQ-9, LACE index, APACHE II, etc.) provide objective data that payers accept as evidence of medical necessity.
  3. Code to the highest specificity. ICD-10 codes should capture the full clinical picture: laterality, type, severity, and stage. Unspecified codes weaken medical necessity arguments.
  4. Document treatment alternatives considered. When a payer denies for medical necessity, they often suggest a less intensive alternative would have been appropriate. Proactively document why alternatives were clinically insufficient.
  5. Conduct quarterly CDI audits. Review denied claims to identify documentation gaps that contributed to denials. Track diagnoses that consistently trigger medical necessity denials and create targeted education for those areas.

The Appeal Letter: Essential Components

A medical necessity appeal letter must be structured, evidence-based, and specific to the payer's coverage criteria. Include:

  1. Patient and claim identifiers — claim number, patient ID, date of service, provider NPI.
  2. The specific denial code and reason — quote the CARC/RARC codes and payer's denial language.
  3. Clinical summary — presenting complaint, examination findings, diagnostic results, and treatment history.
  4. Medical necessity rationale — why this specific service was required for this specific patient, referencing clinical guidelines.
  5. Payer policy citation — reference the payer's own coverage policy and explain how the service meets the stated criteria.
  6. Supporting evidence — clinical guidelines (NCD, LCD, specialty society guidelines), peer-reviewed literature, and parity law citations (for mental health/substance abuse).
  7. Comprehensive medical records — progress notes, lab results, imaging, physician orders, and validated assessment scores.

Medicare Coverage Framework

For Medicare claims, medical necessity is determined through a two-tier framework:

  • National Coverage Determinations (NCDs): Nationwide coverage policies developed by CMS that apply to all Medicare beneficiaries. These take precedence over local determinations.
  • Local Coverage Determinations (LCDs): Regional coverage decisions made by Medicare Administrative Contractors (MACs). These include specific HCPCS and ICD-10 codes that support coverage. When no NCD exists, MACs have authority to pay based on medical necessity or write an LCD.

When appealing Medicare medical necessity denials, always reference the applicable NCD or LCD by number and demonstrate how the clinical documentation meets each stated criterion.

Key Takeaways

  1. CARC 50/96 must be formally appealed — they cannot be resubmitted. You have 120 days from the denial date.
  2. Request peer-to-peer review before filing a written appeal. Peer-to-peer reviews achieve a 78% overturn rate — the highest of any appeal method.
  3. For mental health: cite parity law violations. Appeals with specific parity citations succeed at 3.2x the rate of medical necessity-only appeals.
  4. For physical therapy: cite Clinical Practice Guidelines. CPG-cited appeals achieve an 82% overturn rate.
  5. Invest in CDI programs. Proper clinical documentation is the most cost-effective prevention strategy for medical necessity denials.
  6. Reference payer-specific coverage policies. Always cite the payer's own criteria and demonstrate compliance point by point.

Sources

  • MD Clarity. "Denial Code 50: Explanation & How to Address." mdclarity.com
  • Coronis Health. "Decoding Denial Code CO 50: Medical Necessity Denials." coronishealth.com
  • eTactics. "CO-96 Denial Code: Understanding Non-Covered Charges." etactics.com
  • MediBill RCM. "Top 7 Reasons Mental Health Claims Get Denied." medibillrcm.com
  • Counterforce Health. "Mental Health Insurance Denial: Complete Guide to Appeal Under Parity Laws." counterforcehealth.org
  • Counterforce Health. "How to Win Your Physical Therapy Insurance Claim Appeal." counterforcehealth.org
  • Sirius Solutions Global. "Cardiology Billing Denials: Top Triggers and Prevention." siriussolutionsglobal.com
  • YES HIM Consulting. "Overcoming Medical Necessity Denials with CDI." yes-himconsulting.com
  • American Medical Association. "Fixing Prior Auth: Give Doctors a True Peer Talk, Stat." ama-assn.org
  • National Institutes of Health. "Medicare Coverage: Rules and Standards." PMC, 2024.