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CO-20 Denial Code: Injury Covered by Liability Carrier

CO-20 means the payer believes the injury or illness is covered by a liability carrier, such as the insurer of the person or business responsible for the injury, so the health plan won't pay primary. Bill the liability carrier or show the payer that no liability coverage applies.

Quick facts

Code
CO-20 (CARC 20)
Status
Active In use since January 1, 1995; last modified September 30, 2007.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The payer's usual group. The provider shouldn't bill the patient for it and should pursue the liability carrier or correct the claim.
  • OA (Other Adjustment): Some payers use OA to show neither party is assigned the amount because another carrier is responsible.
  • PR (Patient Responsibility): Occasionally the plan assigns it to the patient. Rules on billing patients with pending liability claims vary by state and contract; check before billing.
Official description
This injury/illness is covered by the liability carrier.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-20 means

CARC 20 says this injury or illness is covered by the liability carrier. When someone else is legally responsible for an injury, their liability insurance may be primary for the related medical bills. Examples include a car accident where another driver was at fault, a fall on someone’s property, or an injury at a business. The health plan uses CO-20 to say it won’t pay primary because a liability insurer should.

The payer may have learned about the liability coverage from box 10b or 10c on the claim, from an accident questionnaire sent to the member, or, for Medicare, from a report that a liability insurer has ongoing responsibility for the diagnosis (N725).

Common causes

  • Accident indicators in box 10b (auto) or 10c (other accident) marked yes, sometimes in error.
  • Liability claim reported to the health plan by the member, attorney, or liability insurer.
  • Injury diagnosis with external cause codes suggesting an accident caused by another party.
  • Missing accident details at intake, so the practice never billed the liability carrier.

How to fix it

  1. Confirm the accident details with the patient: what happened, when, and whether a claim was filed with another party’s insurer.
  2. Collect the liability carrier information: carrier name, claim number, adjuster, and any attorney involved.
  3. Bill the liability carrier or place the account on a lien or letter of protection only if your policies and state law allow.
  4. If no liability coverage applies, or the carrier has denied, send the denial or a written statement to the health plan and request reprocessing.
  5. If the accident indicator was wrong, correct boxes 10a to 10c and send a corrected claim with resubmission code 7 in box 22.
  6. Track the account. Liability claims can take a long time to settle, and health plan filing limits keep running.

How to prevent it

  • Ask every injury patient how the injury happened and record accident type, date, and responsible party.
  • Answer boxes 10a to 10c carefully on each claim.
  • Build an accident case workflow that captures liability, no-fault, and workers’ comp information separately.
  • Watch filing deadlines for the health plan while waiting on the liability carrier. See eligibility and COB denials.

Specialty notes

Emergency medicine, orthopedics, chiropractic, and PT practices treat many accident injuries. Where the liability carrier won’t pay until settlement, some practices rely on attorney liens or letters of protection. Those arrangements have legal and contract implications, so confirm them with counsel and your payer agreements.

Remark codes that may appear with CO-20

  • N725 (A liability insurer has reported having ongoing responsibility for medical services (ORM) for this diagnosis.): A liability insurer has reported ongoing responsibility for medical services for this diagnosis.
  • MA92 (Missing plan information for other insurance.): Information about the other insurance is missing from the claim.
  • CO-21 (This injury/illness is the liability of the no-fault carrier.): The no-fault (PIP) carrier is responsible rather than a liability carrier.
  • OA-19 (This is a work-related injury/illness and thus the liability of the Worker's Compensation Carrier.): The workers' compensation carrier is responsible for a work-related injury.
  • CO-215 (Based on subrogation of a third party settlement): Adjustment based on subrogation of a third-party settlement, which can follow a liability case.
  • CO-P27 (Payment denied based on the Liability Coverage Benefits jurisdictional regulations and/or payment policies.): A liability carrier's own denial under its jurisdictional rules, used on property and casualty remittances.

CO-20 FAQ

What is a liability carrier?

An insurer covering someone's legal responsibility for an injury, such as a driver's auto liability policy, a homeowner's policy, or a business's general liability policy. It pays for injuries its insured caused.

What should I do after a CO-20 denial?

Get the accident details and the liability carrier's name, claim number, and adjuster from the patient or their attorney. Bill the carrier, or if it has denied or there's no coverage, send that information to the health plan and ask it to reprocess.

Can the health plan still pay while the liability case is pending?

Some plans pay and later recover the money through subrogation; others deny until the liability claim is resolved. It depends on the plan and, for Medicare, on conditional payment rules.