Denial Codes

CO-22 Denial Code: Coordination of Benefits, Explained

What CO-22 means, which payer really pays first, and the exact steps to fix the coordination-of-benefits record and get the claim paid.

The CO-22 denial code means the payer believes another health plan should pay this claim first under coordination of benefits (COB). X12, which maintains the code list, defines reason code 22 as “This care may be covered by another payer per coordination of benefits.” The fix is almost never a coding change. It is a coverage question: find out which plan is primary, get the payer records to agree, and bill in the right order.

This page covers the official definition, what the CO group code means for the patient balance, the remark codes that usually ride along, the situations that cause it, and the rebilling sequence. For the other codes in this family, see the denial codes guide.

Updated 2026-10-23. Reviewed by Jacob Greenberg, ClaimCarePro.

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What does CO-22 mean? The official X12 definition

CO-22 is two codes read together: the group code CO and the Claim Adjustment Reason Code (CARC) 22. The X12 CARC list, read on October 23, 2026, gives reason code 22 as “This care may be covered by another payer per coordination of benefits.” It has been on the list since January 1, 1995, and was last modified September 30, 2007 (x12.org).

Note the word “may.” The payer is not saying the claim is wrong. It is saying its records show, or suggest, other coverage that should be billed first. Sometimes that record is right; sometimes it is years out of date. Either way the payer will not pay until the order of benefits is settled.

CO-22 is different from reason code 109, “Claim/service not covered by this payer/contractor. You must send the claim/service to the correct payer/contractor.” Code 109 says you sent the claim to the wrong payer altogether. Code 22 says this payer may owe something, but only after another plan has adjudicated the claim.

What the CO group code means for the patient balance

The CO group code means the adjustment falls under the provider’s contractual obligation, so the CO-22 amount is not a patient balance. X12 says group codes “generally assign responsibility for the adjustment amounts,” and lists CO as Contractual Obligation, PR as Patient Responsibility, OA as Other Adjustment and PI as Payer Initiated Reductions.

In practice an in-network provider cannot move a CO amount onto the patient’s statement. That does not mean the money is lost. Once the primary plan pays and the secondary processes the claim, the remittances will show what, if anything, the patient owes as PR. Bill the patient from those remittances, not from the CO-22 denial. On Medicare claims, CMS’s MLN Matters article SE21002 is explicit: do not bill the beneficiary or send the claim to collections over an inappropriate secondary-payer denial; resolve it with the Medicare contractor.

Remark codes (RARCs) that usually come with CO-22

X12 does not assign remark codes to a reason code. Each payer chooses which Remittance Advice Remark Codes to send. These are the active RARCs whose official wording fits a coordination-of-benefits denial, quoted from the X12 RARC list (read October 23, 2026). Read the remark codes on your own remittance first; they narrow down what the payer wants.

Remark codes that commonly accompany CO-22
RARC	Official X12 text	What it is asking for
MA04	“Secondary payment cannot be considered without the identity of or payment information from the primary payer.”	You billed this payer as secondary but the claim lacks the primary payer or its payment data.
N479	“Missing Explanation of Benefits (Coordination of Benefits or Medicare Secondary Payer).”	The payer wants the primary EOB or the equivalent electronic COB data.
N4	“Missing/Incomplete/Invalid prior Insurance Carrier(s) EOB.”	The prior payer’s data was sent but is incomplete or does not balance.
N598	“Health care policy coverage is primary.”	The payer is telling you which coverage it treats as primary.

Top causes of CO-22 denials

Most CO-22 denials trace back to one of these situations. The Medicare rows come from the CMS Medicare Secondary Payer page; the Florida rows from the Florida Statutes.

Common causes of CO-22 and who pays first
Situation	Who pays first	What to do
Working-aged Medicare patient with employer coverage	If the employer has 20 or more employees, the group health plan pays primary and Medicare pays secondary (CMS MSP rules).	Bill the group health plan first, then Medicare.
Disabled Medicare patient with large-employer coverage	If the employer has 100 or more employees, the group health plan pays primary (CMS MSP rules).	Bill the group health plan first.
End-stage renal disease	A group health plan or COBRA plan pays first during the 30-month coordination period (CMS MSP rules).	Track the coordination period dates; bill the group plan first inside it.
Accident or injury	No-fault or liability insurance pays first for accident-related care; in Florida, PIP benefits are primary (Fla. Stat. 627.736(4)).	Bill the auto or liability carrier first; bill unrelated care on separate claims.
Work injury	Workers’ compensation generally pays first for job-related illness or injury (CMS MSP rules).	Bill the workers’ comp carrier with the claim number.
Two commercial plans (spouse, dependent, COBRA)	Order follows the plans’ COB rules; most follow the NAIC model (own plan before spouse’s, birthday rule for children, active before COBRA).	Ask the patient for both cards and apply the order below.
Medicaid billed first	Florida law makes Medicaid the payer of last resort (Fla. Stat. 409.910(1)).	Bill every other coverage first, then Medicaid.
Stale payer record	The plan has an old “other coverage” entry the patient dropped.	Patient calls the plan (or the BCRC for Medicare) to end the old record, then you request reprocessing.

Who pays first when a patient has two commercial plans?

When neither plan is Medicare, the order usually follows the National Association of Insurance Commissioners (NAIC) Coordination of Benefits Model Regulation. Check the specific plan documents when the result matters: self-funded employer plans can write their own rules. The model applies these rules in order and stops at the first one that decides it:

NAIC model order-of-benefit rules
Situation	Rule in the NAIC model
Own plan vs spouse’s plan	The plan that covers the person as an employee, member or subscriber pays before the plan that covers them as a dependent.
Child of married or cohabiting parents	The birthday rule: the plan of the parent whose birthday falls earlier in the calendar year is primary (month and day, not year).
Child of separated or divorced parents	A court decree that makes one parent responsible for health coverage decides it; without one, the model looks to custody.
Active vs retired or laid-off	The plan covering the person as an active employee pays before the plan covering them as a retiree or laid-off employee.
COBRA or state continuation	The employee or dependent plan pays before the COBRA or continuation plan.
None of the above decide it	The plan that has covered the person longer is primary.

Under the same model, a plan with no coordination-of-benefits provision at all is always primary. That is why a standalone policy without COB language can end up paying first even when the patient thinks of it as “extra” coverage.

How to fix a CO-22 denial, step by step

Read the remark codes and the payer’s COB note. MA04 or N479 means the payer wants primary payment data. No remark code usually means its member file lists another plan.
Verify coverage with the patient. Ask about every plan: their own employer plan, a spouse’s plan, COBRA, Medicare, Medicaid, an auto or work injury claim. CMS tells providers to collect full insurance information at every visit, not just the first.
Settle the order of benefits using the Medicare Secondary Payer rules or the commercial rules above. Run an eligibility check against each plan.
Get the records corrected. If the denying payer is actually primary, the patient updates the plan’s COB record (often a short questionnaire or a member services call). For Medicare, the patient reports the change to the Benefits Coordination & Recovery Center at 1-855-798-2627. Log the date, the rep and the reference number.
Bill the primary plan. Update the patient’s insurance order in your billing system first, so the claim goes to the right payer with the right subscriber data.
Bill the secondary with the primary’s data. Once the primary pays or denies, send the secondary claim carrying the primary’s paid amount and adjustments. The secondary’s remittance will usually show OA-23 for the primary’s impact.
If the payer record was simply wrong, ask the denying payer to reprocess once the patient has corrected it, or appeal with the proof of coverage dates. For Medicare, SE21002 says to contact the contractor and appeal an inappropriately denied claim.

Watch timely filing the whole way. Every payer’s clock is still running while the COB record is being fixed, and a corrected record does not reopen a missed deadline.

How to prevent CO-22 denials

Ask every patient, at every visit, whether their coverage changed: new job, retirement, marriage, Medicare enrollment, an accident or a work injury.
For Medicare patients, use a Medicare Secondary Payer questionnaire at intake. CMS requires providers to determine whether Medicare is primary before billing.
Run eligibility on every plan the patient lists, and read the “other coverage” section of the response, not just active/inactive.
Keep accident and non-accident care on separate claims, with injury-specific diagnosis codes, as SE21002 recommends.
Send a COB reminder to patients whose plans have flagged other coverage before, ahead of their next visit.

Related codes: OA-23 (impact of prior payer adjudication) and CO-197 (authorization absent), which often follows a COB change because the new primary has its own authorization rules.

When to hand CO-22 work to someone else

A single CO-22 is a phone call and a rebill. A stack of them across several payers is a tracking problem: each claim waits on a patient to call a plan, and each has its own timely filing clock. ClaimCarePro’s denial management service reads every denial by reason code and remark code from the 835, works the COB record with the patient and the payer, rebills in the right order, and reports back weekly. Our team brings 30+ years of combined billing experience.

CO-22 questions, answered

What does denial code CO-22 mean?

CO-22 means the payer believes another insurance plan should pay first under coordination of benefits. The X12 description of reason code 22 is “This care may be covered by another payer per coordination of benefits.” The CO group code puts the adjustment under the provider’s contractual obligation, so it is not a patient balance.

Can I bill the patient for a CO-22 denial?

Not for the CO-22 amount itself. CO is the Contractual Obligation group, and an in-network provider generally cannot move a contractual adjustment to the patient. What you can do is ask the patient for the other coverage, bill that plan, and then bill the patient for whatever cost share the remittances assign as patient responsibility.

Is CO-22 the same as a Medicare Secondary Payer denial?

On a Medicare claim it usually is. Medicare returns code 22 when its records show a primary payer such as an employer group health plan, a no-fault or liability insurer, or workers’ compensation. CMS requires every entity that bills Medicare to determine whether Medicare is primary before submitting the claim.

Which remark codes come with CO-22?

X12 does not tie remark codes to a reason code; each payer chooses them. Remark codes whose official wording fits a CO-22 situation include MA04 (secondary payment needs the primary payer’s identity or payment information), N479 (missing explanation of benefits for coordination of benefits or Medicare Secondary Payer) and N4 (missing, incomplete or invalid prior insurance carrier EOB).

How do I fix a CO-22 denial?

Confirm every active plan with the patient, settle which one is primary, get the payer that denied to update its COB record, bill the primary, then send the secondary claim with the primary’s payment and adjustment data. If the denying payer really is primary, have the patient or the other plan correct the record and ask for reprocessing.

Who updates coordination of benefits, the provider or the patient?

Usually the patient. Many plans ask the member to confirm other coverage, often through a COB questionnaire or a call to member services. For Medicare, the patient reports changes to the Benefits Coordination & Recovery Center at 1-855-798-2627. The office can collect the details and prompt the patient, but it rarely can change the payer’s record alone.

Is PIP primary in Florida?

For auto-accident injuries, yes. Florida Statute 627.736(4) says personal injury protection benefits “are primary,” with workers’ compensation benefits credited against them. If a health plan denies an accident claim with code 22, the PIP carrier is usually the payer to bill first.

What is the difference between CO-22 and OA-23?

CO-22 is a denial telling you to bill another payer first. OA-23 shows up after you have done that: it is how the secondary payer reports the impact of the primary payer’s payment and adjustments on its own claim. One starts the COB sequence; the other is the normal sign that it worked.

Denied and aged A/R is worked on a 10% contingency of what is recovered: no recovery, no fee. Ongoing billing is 6% of collections with a $1,000 monthly minimum, denial work included. Details on the pricing page.

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Updated 2026-10-23. Reviewed by Jacob Greenberg, ClaimCarePro.

Sources

X12 Claim Adjustment Reason Codes, read October 23, 2026
X12 Remittance Advice Remark Codes, read October 23, 2026
CMS: Medicare Secondary Payer, read October 23, 2026
CMS MLN Matters SE21002: Billing for Services when Medicare is a Secondary Payer (February 23, 2021)
Medicare.gov: How Medicare works with other insurance
NAIC Coordination of Benefits Model Regulation (October 2013)
Florida Statutes 627.736 (personal injury protection)
Florida Statutes 409.910 (Medicaid third-party liability)