What Are Insurance Denial Codes?
Insurance companies use standardized codes to explain why claims are denied. These codes are called CARC codes (Claim Adjustment Reason Codes).
Two main categories:
- CO codes (Contractual) — Reasons related to your insurance plan's coverage limits. Usually appealable.
- PR codes (Process) — Administrative or procedural reasons. Sometimes appealable, depending on the specific code.
The same code used across all insurance companies means the same thing. CO-50 always means "not medically necessary," whether it's from Anthem, UnitedHealth, or your local plan.
Top 20 Denial Codes & How to Fight Them
- Get clinical guidelines showing your case meets standard criteria
- Physician letter addressing the insurer's specific objection
- Evidence of failed conservative treatment. Check joint replacement appeals or cardiac appeals for examples.
- Request peer-to-peer review (40%+ overturn rate)
- Request medical necessity exception (some plans allow this)
- Verify the benefit max was calculated correctly
- If employer-based, ask employer to increase coverage for essential care
- Request expedited review with additional clinical evidence
- If FDA approved but plan doesn't cover, argue plan language should change
- Get peer-to-peer review
- If emergency, provide documentation of urgency
- Request retroactive prior auth approval
- Some plans excuse emergency prior auth waives
- Request statement of deductible applied to date
- Verify other claims applied to deductible
- Confirm deductible amount in your plan documents
- Resubmit claim with certified confirmation of receipt
- Request claim status update
- Verify your coverage was active on the date of service
- If you were covered, provide proof of coverage
- Verify the procedures were truly separate (distinct anatomical sites, etc.)
- Add modifier codes to unbundle if appropriate
- Get your coder to submit with correct modifiers
- Request exception to bundling rules
- If FDA approved, argue insurer shouldn't override FDA approval
- Provide clinical studies showing it's standard of care
- Peer-reviewed evidence of safety and efficacy
- Resubmit with current insurance card copy
- Request proof of coverage on date of service
- Have billing department verify subscriber ID
Each code points to a specific weakness in your claim. CO-50 says "not medically necessary"—so your appeal must prove medical necessity. PR-96 says "not covered"—so your appeal must show it IS covered under standard guidelines. Match your appeal directly to the code's objection.
Which Denial Codes Are Most Overturnable?
| Code | Reason | Overturn Rate |
| CO-50 | Not medically necessary | 60%+ |
| PR-96 | Service not covered | 40-50% |
| PR-13 | Experimental | 30-50% |
| CO-15 | No prior auth | 15-25% |
| CO-37 | Subscriber unclear | 80-90% |
| PR-1 | Claim lost | 100% |
Why Some Codes Are Easier to Appeal
Most overturnable codes: Subjective rulings (CO-50 "not necessary") or administrative errors (PR-1 "lost claim", CO-37 "subscriber unclear"). These flip when new information is provided.
Least overturnable codes: Absolute plan limits (CO-42 "deductible not met") or plan exclusions. These are harder to fight because they're built into your plan language.
Strategy: Always appeal subjective codes (CO-50, PR-13, PR-96). Don't waste time on absolute plan limits unless you have exception language.
Pro Tip: Get the Code, Then Attack It
If you receive a denial without a specific code, call the insurance company and demand they provide the exact CARC code. Once you know the code, you know exactly what to fight.
Your appeal should be structured as: "We respectfully disagree with [CODE NAME] determination because [specific evidence]."
This shows you understand the system and you're taking it seriously.
If you ever get to litigation or regulatory hearings, you can often discover that insurance company data showing they overturn 50%+ of CO-50 appeals. This data proves the code is subjective. Use it to strengthen your appeal: "Your own data shows these denials are often reversed."