CO-20: Liability Carrier Responsible
The health insurer writes off the claim because a liability carrier is responsible. Redirect the claim to the liability carrier. Do not bill the patient through the health plan.
What Does CO-20 Mean?
CO-20 is the standard pairing for this denial. The CO designation means the health insurer is declining coverage as a contractual obligation because a liability carrier should be primary. You cannot bill the patient through the health plan for this denied amount. The claim must be redirected to the liability carrier. If the liability carrier ultimately does not cover the charges — because their coverage is exhausted, the claim is disputed, or no liability carrier actually exists — you may then return to the health insurer with documentation supporting that the health plan should process the claim.
When CARC 20 shows up on a remittance, the health insurer is declining payment because the injury or illness is linked to a liability claim. This typically involves automobile accidents, slip-and-fall incidents, dog bites, product liability injuries, or any situation where a third party's insurance — not the patient's health plan — bears financial responsibility for the medical expenses. The health insurer is saying: someone else's insurance should pay for this.
The denial is triggered when the payer's system detects indicators of a liability-covered event, often through diagnosis codes associated with injuries (motor vehicle accident codes, external cause codes), the patient's own disclosure on intake forms, or information from other payers in the coordination of benefits chain. Unlike workers' compensation denials (CARC 19), CARC 20 specifically points to liability insurance — the type of coverage that pays when one party is legally liable for another's injuries.
Redirecting these claims requires a different workflow than standard health insurance billing. Liability carriers operate on fundamentally different timelines — personal injury claims can take months or years to settle — and they may require pre-authorization, attorney liens, or letters of protection before paying medical bills. Providers who regularly treat accident and injury patients need established processes for identifying liability coverage at intake and managing the extended billing cycle these claims typically involve. If the liability carrier's coverage is exhausted, you can then submit to the patient's health insurance with documentation of the exhausted benefits.
Common Causes
| Cause | Frequency |
|---|---|
| Injury related to an auto accident or third-party liability The patient's injury or illness stems from an automobile accident, slip-and-fall, or other incident where a third-party liability carrier (auto insurance, homeowner's insurance, commercial liability) is responsible for covering the medical expenses | Most Common |
| Claim submitted to wrong insurance carrier The provider filed the claim with the patient's health insurance instead of the liability carrier that covers the incident-related medical expenses | Most Common |
| Missing liability carrier documentation The claim lacks required supporting documentation such as accident reports, police reports, witness statements, or injury circumstance details that the liability carrier needs to process the claim | Common |
| Liability carrier not identified during intake Registration staff failed to identify that the visit was related to a liability claim and did not collect the liability carrier's information, policy number, or claim number | Common |
| Pre-authorization not obtained from liability carrier Some liability carriers require pre-authorization for treatment; the provider proceeded without obtaining required approval from the liability insurer | Occasional |
| Liability carrier reached coverage limits The liability insurance policy has reached its coverage limits for the incident, and the remaining charges need to be redirected to the patient's health insurance or to the patient directly | Occasional |
How to Resolve
Confirm the injury involves a liability carrier, obtain their claim information, and redirect the claim to the correct payer — or dispute the classification if it was applied in error.
- Verify liability involvement and collect carrier details Confirm the injury involves a third-party liability carrier and obtain the carrier name, policy number, claim number, and adjuster contact information.
- Submit to the liability carrier with full documentation File the claim with the liability carrier including accident reports, medical records, and detailed injury documentation following their submission guidelines.
- Dispute if liability classification is incorrect If no liability carrier is involved, contact the health insurer with supporting documentation to overturn the denial. Provide patient statements and clinical records demonstrating the condition is not liability-related.
- Resubmit to health insurer if liability coverage is exhausted If the liability carrier's limits are reached, obtain documentation of exhausted benefits and resubmit to the health plan with proof of depleted coverage.
Common RARC Pairings
The RARC code tells you exactly what triggered the CO-20:
| RARC | Description |
|---|---|
| N381 | Alert: Consult your contractual agreement for restrictions, billing, and payment information related to these charges. |
| N479 | Alert: This claim may be covered by another carrier. Contact the appropriate liability carrier for submission. |
How to Prevent CO-20
- Screen every injury-related visit at intake for potential liability carrier involvement, including auto accidents, falls on others' property, and other third-party incidents
- Collect liability carrier information during registration before rendering services for any injury that may involve a third party
- Document injury circumstances thoroughly in the medical record including how, when, and where the incident occurred
- Verify liability carrier coverage and pre-authorization requirements before providing non-emergency services
- Maintain processes for managing liability claims' extended payment timelines including liens and letters of protection
General Prevention
- Screen every injury-related visit at intake to determine if a liability carrier (auto insurance, homeowner's insurance, commercial liability) is involved
- Collect liability carrier information including carrier name, policy number, claim number, and adjuster contact details during patient registration
- Document the circumstances of the injury in the medical record including how, when, and where it occurred to support proper claim routing
- Verify liability coverage and pre-authorization requirements before providing services when a liability carrier is identified
- Maintain current knowledge of state-specific liability insurance claim filing requirements and deadlines
Also Filed As
The same CARC 20 may appear with different Group Codes:
Related Denial Codes
Sources
- https://www.mdclarity.com/denial-code/20
- https://docs.claim.md/docs/claim-adjustment-reason-codes
- https://practiceperfectss.com/list-of-denial-codes-in-medical-billing/
- Codes maintained by X12. Visit x12.org for official definitions.