CO-20 denial code
This injury is covered by the liability carrier
How to fix it
Identify the liability carrier and claim number and bill them. Where liability is disputed, some plans pay pending subrogation.
How to prevent it
Capture accident details and any third-party carrier at registration for injury-related visits.
In practice
A patient is treated after a slip and fall at a retail store. The health plan returns CO-20, taking the position that the premises liability carrier is responsible for the injury.
Liability coverage does not work like health insurance. There is no member card, no eligibility file to query, and often no accepted claim at the time care is delivered — the carrier may take months to decide whether it accepts responsibility at all.
The workable path is to obtain the carrier name, claim number and adjuster from the patient, bill the carrier, and where liability is contested, ask the health plan to pay pending subrogation. Many plans will, and the alternative is an account that ages indefinitely while two carriers point at each other.
What sits behind it
Understanding why plans do this makes the denial easier to work. Health plans hold a contractual right of subrogation, recovering what they paid if a liable party is later established, and denying up front rather than paying and recovering shifts both the cost and the effort onto the provider.
The practical risk is time. Liability settlements routinely take a year or more, and the filing deadline with the health plan runs from the date of service regardless. An account parked in a liability queue is quietly ageing toward a timely filing denial that will not be reversible.
The protective move is to bill the health plan in parallel and document the liability position rather than choosing between them. Where a plan refuses to pay pending resolution, having the denial on record within the filing window preserves the appeal that would otherwise be lost.
Related codes
Terms used here — Coordination of Benefits · Timely Filing · Patient Responsibility
How we handle it — AR Management · Denial Management · Patient Collections
Primary sources
The rules behind CO-20, at the bodies that publish them.
- Workers' compensation medical billing (opens in a new tab)
US Department of Labor, OWCP — Federal workers' compensation fee schedule and billing requirements. State programs differ, but the structural rules are the same: a separate payer with its own schedule.
- Medicare Secondary Payer Manual (opens in a new tab)
Centers for Medicare & Medicaid Services — When Medicare pays second, and to whom the claim goes first. Coordination-of-benefits denials are resolved here rather than with the patient.
- Medicare Claims Processing Manual (opens in a new tab)
Centers for Medicare & Medicaid Services — The operative manual for how Medicare claims must be coded, submitted, adjusted and appealed. When a payer policy and a vendor's advice disagree, this settles it.
Looking for a different code? Search all 190 CARC and RARC codes
Questions about CO-20
No. Settlements often take a year or more while the health plan's filing deadline runs from the date of service, so waiting converts a coordination question into a permanent timely filing denial. Bill both, document the liability claim, and let the carriers resolve responsibility between themselves.
The liability carrier's name, the claim or file number, the adjuster's contact details, and the date of the incident. Collecting this at registration for any injury-related visit is far easier than reconstructing it weeks later once a denial has already arrived.
Check the plan contract and state law before doing so, because many jurisdictions restrict balance billing where a liability claim is pending, and some prohibit it entirely. Where an attorney is involved, a letter of protection is the usual mechanism and is worth requesting early.
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