What does CO-22 mean?

CO-22 is a Contractual Obligation (CO) denial: "This care may be covered by another payer per coordination of benefits." The payer believes another insurance is primary and should be billed before them.

CO · Contractual ObligationCARC 22

Denial Code CO-22

Q: Is CO-22 the patient's responsibility or a provider write-off?

CO-22 carries the CO group code (Contractual Obligation): Provider/contractual responsibility — not billable to the patient while denied. A CO adjustment is the provider's responsibility, not the patient's: balance-billing the patient for a CO amount is a contract (and often compliance) violation. But CO does not automatically mean “write it off.” When the cause is fixable — missing information (CO-16), a modifier problem (CO-4), or NCCI bundling (CO-97) — you correct and resubmit, or appeal with documentation. You only truly write the amount off when it is a final contractual adjustment, such as the fee-schedule difference on CO-45.

This care may be covered by another payer per coordination of benefits.

Source: X12 Claim Adjustment Reason Codes (CARC) & Group Codes. Maintained by the D3rx Clinical Billing Team.

What CO-22 means

The payer believes another insurance is primary and should be billed before them.

Got this denial right now?

Fix & resubmit: see the CO-22 correction steps

See CO-22 correction steps Ask D3 about CO-22

CO-22 clears with a corrected claim, not an appeal. Ask D3 walks you through the exact fix — free, no signup.

CO group code: who absorbs the charge

Contractual Obligation — Provider/contractual responsibility — not billable to the patient while denied.

A CO adjustment is the provider's responsibility, not the patient's: balance-billing the patient for a CO amount is a contract (and often compliance) violation. But CO does not automatically mean “write it off.” When the cause is fixable — missing information (CO-16), a modifier problem (CO-4), or NCCI bundling (CO-97) — you correct and resubmit, or appeal with documentation. You only truly write the amount off when it is a final contractual adjustment, such as the fee-schedule difference on CO-45.

Why CO-22 happens

The patient has more than one active plan and the claim went to the secondary payer first
Medicare Secondary Payer (MSP) rules apply (e.g., the patient or spouse has active employer group coverage)
Coordination-of-benefits (COB) information on file with the payer is stale or shows another plan as primary
A liability, auto, or workers' compensation carrier should be primary for the injury-related service

What to do when you get CO-22

1Confirm the correct payer order with the patient and verify eligibility on each plan
2If this payer is truly secondary, bill the primary first, then submit to this payer with the primary's EOB/ERA attached
3If this payer IS primary, have the patient (or payer) update the COB record, then resubmit
4For MSP situations, complete the MSP questionnaire and bill in the correct order

Appeal, correct, or write off CO-22?

CO-22 is a routing/coordination problem, not a medical-necessity denial, so the cure is usually a corrected submission rather than an appeal: send the claim to the primary payer first, then resubmit here with the primary remittance attached. Only file an appeal if you have proof this payer is in fact primary and the COB record is wrong despite being corrected.

Timing & deadlines

Secondary claims still must land within this payer's timely-filing limit measured from the date of service (often ~90-180 days commercial; Medicare 12 months), so do not let the primary adjudication run out the clock. Many payers allow a COB exception window once the primary EOB date is documented.

Example

A working-aged patient covered by both a spouse's employer plan and Medicare is billed to Medicare first. Under MSP, the employer group health plan is primary, so Medicare returns CO-22. Billing the commercial plan first and then submitting to Medicare with that EOB resolves it.

Prevent CO-22 going forward

Ask about all active coverage at every check-in, not just the first visit
Run an MSP questionnaire for Medicare patients who are still working
Verify primary/secondary order electronically before submitting
Keep COB records refreshed annually for patients with multiple plans

Code families most affected

All services for dual-coverage patients
Medicare claims subject to MSP
Injury-related services where auto/workers' comp may be primary

Related codes

Denial codes you'll often see alongside CO-22

OA-23 CO-109 PR-1

Payer notes

COB rules are standardized in concept (NAIC model), but each payer maintains its own COB record and update process. The fastest fix is often a direct call to update which plan is primary; the specific exception window for late COB filing varies by payer.

Fix this CO-22 denial the right way

CO-22 is resolved with a corrected claim, not an appeal. Ask D3 gives you the exact correction steps — free, backed by CMS, Medicare, and major-payer data.

See CO-22 correction steps Ask D3 about CO-22 All denial codes

Medical billing disclaimer

CARC/RARC definitions are the standardized X12 set; group-code semantics follow the X12 Claim Adjustment Group Code standard. Filing and appeal windows vary by payer — the standard anchors shown (Medicare redetermination 120 days from the remittance; Medicare timely filing 12 months from date of service; most commercial payers ~90-180 days) are general references, not a guarantee for any specific plan. Always confirm the rule in the payer's provider manual before acting. D3rx is not responsible for claim outcomes.