OA 20 denial code

Claim adjustment reason code 20. Often reported as OA 20 or CO 20.

Liability insurer is responsible

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What 20 means

The payer considers the injury the responsibility of a liability carrier, such as another party's insurance.

The payer has decided that a liability policy, for example a property owner's or another driver's insurer, should cover this injury. It is a coordination issue, not a statement that the care was wrong.

Rules on whether the health plan pays first and recovers later vary by plan and by state, so check the payer's policy before deciding where to bill.

Group codes seen with 20

On a remittance, 20 comes after a group code. These are the ones it is most often reported with:

• OA 20 (Other Adjustment): Used for adjustments that are neither the provider's contractual write-off nor the patient's share. It often appears with coordination of benefits, for example when another payer already paid.
• CO 20 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The claim had accident indicators showing an injury caused by another party.
• The payer learned of a liability claim from the patient or another source.
• The patient has not returned a questionnaire about how the injury happened.

What to do next

1. Ask the patient how the injury happened and whether a liability or legal claim is open.
2. Bill the liability carrier if the payer's policy requires it to pay first.
3. Help the patient complete any accident questionnaire the plan sent, then ask for reprocessing.
4. Correct accident indicators and resubmit if the injury was not caused by another party.

Related codes

• 19 (reason code) Workers' compensation is responsible
• 21 (reason code) No-fault insurer is responsible
• 22 (reason code) Another payer may be primary