CO-22 Denial Code: Why Your Claim Was Denied and How to Fix It

Denial code CO-22 in medical billing means the insurance company thinks another insurance plan should pay the claim first. Once that insurer processes the claim, the second insurance company can check how much of the remaining amount it covers.

This often happens when a patient has more than one insurance plan, such as Medicare and employer coverage. Insurance companies keep information about which plan should pay first in their coordination of benefits (COB) records.

If you send the claim to the secondary insurer before the primary one, you may receive a CO-22 denial. The same can happen when the insurance company’s COB records are wrong or outdated, even if you’ve billed the correct insurer.

Simply resubmitting the claim won’t fix either problem. You first need to confirm which insurance should pay first and whether the payer has the correct information. If the records are wrong, the patient may need to contact their insurance company to get them updated.

Quick Takeaways

What Is the CO-22 Denial Code?

CO-22 is a coordination of benefits (COB) denial that tells you the payer believes another insurance plan may be responsible for the claim.

To understand it, you need to know what coordination of benefits means.

When a patient has two or more insurance plans, COB rules determine which plan pays first. The primary payer processes the claim first, while the secondary payer considers any remaining eligible costs according to its coverage rules.

For example, a patient has Medicare and insurance through their current employer. You submit the claim to Medicare, but Medicare’s records show the employer plan should pay first. Medicare returns CO-22.

You’ll usually find CO-22 on the payer’s Explanation of Benefits (EOB) or Electronic Remittance Advice (ERA). The ERA comes through an 835 transaction, which carries payment and denial details, while the original claim is submitted through an 837 transaction.

One thing to remember: CO-22 doesn’t prove another plan is actually primary. It tells you what the denying payer’s records indicate. Your job is to verify whether those records are correct.

CO-22 Denial Code Description

The official description of Claim Adjustment Reason Code (CARC) 22, maintained by X12, is:

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

Notice the word may. The payer is indicating a possible responsibility for another insurer, not necessarily confirming that the other insurer will pay.

The number 22 is the reason code (or the CARC) and tells you why the claim was adjusted: another insurance plan may need to pay first. The letters before it, such as CO or PR, are a group code. They tell you whether the payer considers the adjustment a Contractual Obligation or Patient Responsibility.

If you want to understand other common denial codes, our denial codes in medical billing guide explains what they mean and how to handle them.

CO-22 vs PR-22 and OA-22

As you can already tell, the three adjustment codes CO-22, PR-22, and OA-22 all share the same underlying reason code, but the group codes mean different things.

The group code tells you whether the insurance company considers the adjustment a contractual obligation (CO), patient responsibility (PR), or another type of adjustment (OA).

Code	What it means	Can you bill the patient?
CO-22	The unpaid amount is treated as a contractual obligation, not patient responsibility.	No. Resolve the COB issue first.
PR-22	The insurer has marked the unpaid amount as patient responsibility.	Not automatically. Check whether the patient actually owes the amount before billing.
OA-22	The unpaid amount is classified as an other adjustment, rather than CO or PR.	Not based on this code alone. Review the payer’s information first.

One thing worth paying attention to is PR-22. Although PR stands for Patient Responsibility, it doesn’t automatically mean the patient owes the unpaid amount. Before sending them a bill, check which insurance should pay first and whether the claim needs to go through another payer. Once the insurance issue is sorted out, you can determine if the patient actually owes anything.

Remark Codes You May See With CO-22

A CO-22 adjustment tells you there’s a potential payer-order problem. The accompanying remark codes may help explain what information is missing or how the claim was handled.

Here’s the distinction: CARCs explain why a claim was adjusted, while Remittance Advice Remark Codes (RARCs) provide additional information.

You’ll find these codes on the payer’s remittance advice. If you need help reading them, our ERA medical billing guide explains what the codes mean and how to read the payment details.

Remark code	Meaning	What the biller should do
MA04	The primary payer’s identity or payment information is missing or unreadable.	Verify the primary payer and submit the required payment information.
N598	Another health insurance policy is primary.	Confirm that coverage and bill in the correct order.
MA18	The claim information has been forwarded to the patient’s supplemental insurer.	Check whether the secondary claim crossed over before billing again.
N89	Payment information was forwarded to multiple payers, but only one can be identified on the remittance.	Check which insurers received the information.

MA18 and N89 are informational alerts about claim forwarding. They aren’t necessarily additional reasons for a CO-22 denial.

What Does CO-22 With MA04 Mean?

CO-22 with MA04 generally means the payer cannot consider secondary payment because it doesn’t have enough information about the primary insurance.

For example, you submitted a claim to Medicare as the secondary payer but left out the primary insurer’s payment details.

The first thing to check is the primary EOB and the information transmitted on the secondary claim. Correct what’s missing and follow the payer’s resubmission instructions.

Why Do CO-22 Denials Happen? 

Most CO-22 denials happen because the insurance company has different information about the patient’s coverage than what’s on the claim. Sometimes, it’s an outdated insurance record. Other times, the claim was simply sent to the wrong payer first.

Here are six common situations that can lead to a CO-22 denial:

1. Other insurance was missed. The patient has insurance through their employer but only provides their Medicare card. You bill Medicare without knowing another plan may need to pay first.
2. Outdated COB information. The patient left their job months ago, but Medicare still has their old employer’s insurance listed as active. As a result, Medicare continues to deny claims that it should potentially be paying.
3. Wrong billing order. The patient has two active insurance plans, but the claim was sent to the secondary insurer instead of the one that should pay first.  
4. The primary EOB is missing. You submit a claim to the secondary insurer without including the primary payer’s payment or adjustment details. The secondary insurer doesn’t have the information it needs to process the claim.
5. Medicare is supposed to pay second. The patient has coverage through a current employer, qualifies under certain disability-related coverage rules, or has another insurance arrangement that makes Medicare secondary.
6. Medicaid was billed before other insurance. The patient has another insurance plan that may be responsible for the claim, but Medicaid receives it first.

Here’s something worth checking before you do anything else: Look at the patient’s insurance coverage on the actual date of service, not just what shows as active today. A patient may have changed jobs or insurance plans since their appointment, and that difference could explain the denial.

Medicare CO-22: When Does Medicare Pay Second? 

Medicare doesn’t always pay first, even when a patient is enrolled in it. If you receive a CO-22 denial from Medicare, it usually means Medicare’s records show another insurance plan should have paid the claim first.

This is where Medicare Secondary Payer (MSP) rules come in. These rules, set by the Centers for Medicare & Medicaid Services (CMS), determine when Medicare pays after another insurer, such as an employer health plan or workers’ compensation.

Whether Medicare pays first or second depends on the patient’s insurance coverage, employment status, and sometimes the size of their employer.

When Does Medicare Pay Second?

The table below shows common situations where another insurer pays before Medicare.

Situation	Who pays first?
Working aged (65 or older): The patient has insurance through their current job or their spouse’s job, and the employer has 20 or more employees.	Employer health plan
Working aged (fewer than 20 employees): The employer has fewer than 20 employees, subject to applicable exceptions.	Generally Medicare
Disability (under 65): The patient has Medicare due to disability and insurance through their own or a family member’s current job with an employer of 100 or more employees.	Large employer health plan
End-stage renal disease (ESRD): The patient is within the 30-month coordination period, regardless of employer size.	Group health plan, including qualifying COBRA or retiree coverage
Workers’ compensation: The patient receives treatment for a work-related injury or illness.	Workers’ compensation insurance
No-fault or liability insurance: The treatment is related to an accident covered by one of these policies.	Responsible no-fault or liability insurer
Federal Black Lung benefits: The treatment is covered under the Black Lung Program.	Federal Black Lung Program
Retiree coverage or COBRA: The patient has retiree insurance or COBRA coverage outside applicable ESRD circumstances.	Generally Medicare

You can find more details in the CMS Medicare Secondary Payer guidance.

These are the general rules, but exceptions do exist, especially for certain employer plans and accident-related claims. So, before billing Medicare, make sure you’ve checked the patient’s coverage and confirmed which insurance should pay first.

How Do You Verify Medicare’s Primary or Secondary Status?

Before you resubmit a CO-22 claim to Medicare, make sure you know whether Medicare should actually pay first or second.

Start by reviewing the patient’s Medicare Secondary Payer (MSP) Questionnaire. It helps you check whether the patient has insurance through an employer, coverage related to an accident, or any other insurance that may need to pay before Medicare.

Next, check Medicare’s records through your Medicare Administrative Contractor (MAC) portal. Depending on your location, your MAC may be First Coast, CGS, or Noridian.

If Medicare still shows an old insurance plan as primary, the patient will need to contact the Benefits Coordination & Recovery Center (BCRC) at 1-855-798-2627 to get the information corrected.

You can help the patient gather the necessary details, but updating the insurance information in your billing system won’t automatically change Medicare’s records.

Once the records are corrected, follow your MAC’s instructions to resubmit the claim. If another insurance plan is correctly listed as primary, bill that insurer first and then send the claim to Medicare for secondary payment.

One more thing: Don’t confuse a CO-22 denial with CO-24. If a patient is enrolled in a Medicare Advantage plan and you bill Original Medicare instead, you may receive CO-24. We’ll explain the difference later in the article.

How Commercial Insurance Decides Who Pays First 

When a patient has two commercial insurance plans, figuring out which one to bill first can be confusing. A patient might have coverage through their own employer and their spouse’s plan. Or a dependent child might be covered under both parents’ insurance plans.

In situations like these, insurance companies use coordination of benefits (COB) rules to decide which plan pays first.

The National Association of Insurance Commissioners (NAIC) has a Coordination of Benefits Model Regulation that many states use as a basis for their rules, although the exact requirements can vary by state and insurance plan.

Here’s a quick look at how the most common rules work.

COB rule	Which insurance pays first?
Employee vs. dependent coverage	Insurance through the patient’s own job generally pays before coverage through a spouse or parent.
Birthday rule	When a dependent child is covered by both parents’ plans, the plan of the parent whose birthday comes earlier in the year usually pays first.
Divorced or separated parents	A court order may decide which plan pays first. Without one, the custodial parent’s plan generally comes first under the NAIC model rules.
Active employee vs. retiree coverage	Insurance through a current job generally pays before retiree coverage when this rule applies.
COBRA coverage	Insurance through qualifying active employment generally pays before COBRA when the applicable COB rule applies.
Longer coverage	If the other rules don’t settle it, the plan that has covered the patient longer generally pays first.

The Birthday Rule for Coordination of Benefits

Let’s say you’re billing for a child who’s covered under both parents’ health insurance plans. Which one should you bill first?

This is where the birthday rule comes in.

The rule looks at both parents’ birthdays to determine which insurance is primary. For example, if the mother’s birthday is March 15 and the father’s is October 10, the mother’s plan generally pays first because her birthday comes earlier in the calendar year.

It doesn’t matter which parent is older. Only the month and day of their birthdays count.

If both parents have the same birthday, the plan that has covered the parent longer generally pays first.

What If the Parents Are Divorced or Separated?

Things work a little differently when the parents are divorced or separated.

First, check whether there’s a court order that addresses the child’s health insurance. If it identifies which parent is responsible for coverage, that may determine which plan pays first once the insurer has the required information.

If there’s no applicable court order, the NAIC model rules generally follow this order:

1. The custodial parent’s insurance
2. The custodial parent’s spouse’s insurance
3. The other parent’s insurance
4. The other parent’s spouse’s insurance

So, before applying the birthday rule, check whether a court order or custody arrangement changes which plan should pay first.

Active Employment, Retiree Coverage, and COBRA

Here’s another situation that can cause confusion: a patient has insurance through a current job but also has retiree coverage or COBRA from a previous employer.

Which one should you bill first?

Under applicable COB rules, insurance through active employment generally takes priority over retiree or COBRA coverage.

For example, a patient still has COBRA from their previous job but recently started a new job with health insurance. The new employer’s plan may be primary, even though the COBRA coverage started earlier.

There’s one more thing to watch for. Self-funded employer plans, which are generally governed by the Employee Retirement Income Security Act (ERISA), aren’t subject to state insurance regulations in the same way fully insured plans are. Their COB provisions may differ, so check the plan documents before deciding the billing order.

When you’re dealing with two commercial plans, it’s worth confirming the primary payer before submitting the claim. Our guides on Blue Cross Blue Shield billing and out-of-network insurance can also help you understand other plan-specific billing requirements.

How Medicaid, TRICARE, and Other Plans Pay 

Some insurance programs have their own rules about who pays first. So, if your patient has Medicaid, TRICARE, Medicare Advantage, or Medigap, it’s important to know how each one works before submitting a claim.

Here’s a quick breakdown to help you get the billing order right.

Coverage	How payment generally works
Medicaid	Usually pays after other insurance. However, some services follow special billing rules.
TRICARE	Generally pays after other health insurance, except Medicaid and certain other programs. Different rules apply to active-duty service members.
Medicare Advantage	Most covered claims go to the patient’s Medicare Advantage plan, not Original Medicare. Billing Original Medicare instead may result in CO-24.
Medigap	Helps pay certain costs left after Original Medicare processes the claim.
VA benefits	Medicare and VA generally don’t pay for the same service. Which program pays depends on where and how the patient received care.

CO-22 Denial Code Medicaid: Why It Happens and How to Fix It

Medicaid is generally the payer of last resort. In simple terms, if a patient has another insurance plan that’s responsible for the bill, that plan usually needs to pay before Medicaid.

Let’s say a patient has Medicaid along with health insurance through their employer. You submit the claim to Medicaid first, but Medicaid’s records show the employer’s plan as primary. This could result in a CO-22 denial.

So, how do you fix it?

First, check the patient’s other insurance coverage and Medicaid’s third-party liability (TPL) records. These records help Medicaid identify other insurers or parties that may be responsible for paying the claim.

If Medicaid still shows an old insurance plan or incorrect coverage information, ask the patient to report the change to their state Medicaid agency or managed care plan. You should also contact the payer to find out what information or documents are needed to correct the record.

Once the issue is resolved, follow the state’s instructions to bill the correct insurer or resubmit the claim.

One thing worth knowing: Medicaid doesn’t always require another insurance company to pay first. Certain services, such as qualifying preventive care for children, may follow what’s called a pay-and-chase rule. This means Medicaid can pay the provider first and then recover the money from the responsible insurer.

Since Medicaid billing rules can differ by state and program, it’s always worth checking the payer’s requirements before submitting the claim again.

How to Fix a CO-22 Denial 

Got a CO-22 denial? Before you resubmit the claim, find out why the insurance company thinks another payer should pay first. Sending the same claim again without fixing the issue will likely lead to another denial.

Here’s a quick plan to get things moving.

Step 1: Check the Denial Details

Start with the EOB or ERA. Look at the denial reason, any accompanying remark codes, and the date of service.

For example, CO-22 with MA04 may mean the payer is missing information about the primary insurance. Knowing exactly what the payer needs will help you decide what to do next.

Step 2: Verify the Patient’s Insurance

Check all the insurance plans the patient had on the date of service, not just the ones showing as active today.

Confirm the member ID, policyholder details, and coverage dates. Ask whether the patient had insurance through an employer, spouse, Medicare, Medicaid, or another plan.

Don’t rely only on the insurance cards in your system. The patient’s coverage may have changed since their last visit.

Step 3: Confirm Which Insurance Pays First

Now check which plan should be primary.

For Medicare, review the patient’s MSP status. For commercial insurance, check the applicable COB rules, such as employee coverage or the birthday rule.

If you’re still unsure, call the insurance companies and ask them to confirm which plan their records show as primary for that date of service.

Before ending the call, get a reference number and document what the payer tells you. You’ll have something to refer to if the claim gets denied again.

Step 4: Get the COB Information Corrected

If the insurance company’s records are wrong, the next step is to get them corrected.

Usually, the patient or policyholder needs to contact their insurer to update the COB information. You can guide them through what needs to be fixed, but updating your billing system won’t automatically update the insurance company’s records.

Here’s who to contact:

Payer	Who can update the COB information?
Medicare	The patient or authorized representative contacts the BCRC. You can check the MSP status through your MAC portal.
Commercial insurance	The patient or policyholder usually contacts the insurer’s COB department. You can help provide supporting documents if needed.
Medicaid	The patient reports coverage changes to their state Medicaid agency or managed care plan. The agency or plan updates the records.

Step 5: Bill the Primary Insurance First

Once you’ve confirmed which insurance is primary, submit the claim to that payer.

Wait for the primary insurer to process it and provide an EOB showing what was paid, adjusted, or denied. You’ll need those details when billing the secondary insurance.

If the primary claim is denied, check why before moving on. Don’t assume the secondary insurer will automatically pay it.

Step 6: Submit the Claim to Secondary Insurance

Once the primary insurer has processed the claim, you can bill the secondary insurer. Make sure to include the payment and adjustment details from the primary EOB so the secondary insurer knows what has already been paid.

But before submitting the claim, check whether it has already been sent automatically through a crossover. This commonly happens between Original Medicare and certain supplemental insurance plans.

A practical tip for billing managers: Make sure your payment posting team checks for crossover claims before sending them to secondary insurance. At A2Z Medical Billing Services, this is part of our payment posting process. If a claim has already been forwarded, our team tracks its status instead of submitting it again.

This helps avoid duplicate submissions and keeps secondary claims from getting lost in the follow-up process. It’s one part of our broader billing work, where clients have reported fewer billing errors, quicker reimbursements, and improved claim processing.

Step 7: Follow Up Until the Claim Is Paid or Resolved

Once you’ve submitted the corrected claim, don’t leave it there.

Check that the insurer received and accepted it. Follow up on the claim’s status and keep it in your A/R worklist until you receive a final payment or denial decision.

If the claim gets denied again, review the new denial reason before taking further action.

If your team is spending too much time following up on unpaid claims, A2Z’s A/R follow-up services can help you manage payer follow-ups, claim corrections, and outstanding balances.

When Should You Appeal a CO-22 Denial?

An appeal is useful when an insurance company denies a claim incorrectly and you need them to reconsider their decision. If the appeal is successful, the payer may overturn the denial and process the claim for payment.

For CO-22, an appeal may be appropriate when you’ve billed the correct insurance, the COB records are accurate, but the payer still refuses to process the claim.

However, if the denial happened because you billed the wrong insurance or left out the primary payer’s information, it’s usually better to correct the issue and resubmit the claim.

Before filing an appeal, gather these documents:

• Original denial or remittance advice
• Verified insurance coverage dates and primary payer details
• Proof of updated COB information, if applicable
• Primary payer’s EOB
• Previous claim submissions and payer correspondence

Also, check the insurer’s appeal deadline. For Original Medicare, the first level of appeal is called a redetermination, and you generally have 120 days from receiving the initial decision to request one.

Keep in mind: An appeal won’t automatically fix outdated COB records. If the insurance information is wrong, get that corrected first so you’re not appealing a denial without addressing what caused it.

Does CO-22 Affect Timely Filing?

A CO-22 denial doesn’t give you extra time to file a claim. Even if you’re waiting for the patient or insurance company to fix the COB information, the filing deadline stays the same.

For Original Medicare, you generally have 12 months from the date of service to submit a claim. Deadlines for commercial insurance and Medicaid depend on the payer, plan, and state.

So, when a CO-22 denial comes in, check how much time you have left before the filing deadline.

Keep copies of your original claim, proof that it was submitted and accepted, denial notices, and any communication with the insurance company. You may need these records if there’s a dispute over when the claim was filed.

What if the deadline has already passed? Check whether the payer allows an exception. Medicare only allows exceptions in limited situations, and a denial for late filing generally can’t be appealed. Commercial insurance and Medicaid rules vary, so contact the payer to find out what options you have. 

You don’t want to spend weeks getting the COB information corrected, only to find out it’s too late to send the claim again.

How Is CO-22 Different From Other Denial Codes? 

Some denial codes can look similar to CO-22, but they point to different problems. Knowing the difference helps you figure out what went wrong and what to fix before sending the claim again.

Here’s a quick comparison of commonly related codes.

Code	What it means
CO-22	Another insurance plan may need to pay first under coordination of benefits rules.
OA-23	The claim amount was adjusted based on payments or adjustments made by a previous insurer.
CO-24	The charges are covered under a capitation or managed care agreement.
CO-109	The claim was sent to a payer that doesn’t cover the service. Check which payer should receive it.
CO-19	The claim is related to a work injury or illness that workers’ compensation is responsible for.
CO-27	The patient’s insurance coverage ended before the date of service.
CO-16	The claim has missing or incorrect information that needs to be fixed.
CO-29	The claim was submitted after the payer’s filing deadline.

The next step depends on the code. For example, CO-19 means you need to check workers’ compensation coverage, while CO-22 means you need to find out which insurance should pay first.

Other codes, such as CO-45 for charges above the allowed amount and CO-197 for missing authorization, involve different billing problems and need a different approach.

How to Prevent CO-22 Denials

Most CO-22 denials can be avoided by checking the patient’s insurance information before submitting the claim. It starts at the front desk, where a missed insurance plan or an outdated coverage record can cause problems later.

Here are six things your team can do to reduce these denials:

A few extra checks during registration can save your billing team hours of correcting claims and calling insurance companies.

If your practice needs help with these checks, A2Z’s insurance verification services can help catch coverage problems before claims go out.

Frequently Asked Questions

What does denial code CO-22 mean?

CO-22 means the insurance company believes another insurance plan may need to pay the claim first. This usually happens when a patient has more than one insurance plan or the payer has outdated coverage information. Check which insurance is primary and whether the payer’s records need to be corrected before resubmitting the claim.

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

No, you shouldn’t bill the patient just because a claim was denied with CO-22. First, find out which insurance should pay and get the claim processed in the correct order. Once both insurers have processed the claim, check whether the patient owes anything under their coverage and the applicable billing rules.

What is the difference between CO-22 and PR-22?

Both codes mean another insurance plan may need to pay first. The difference is how the insurer treats the unpaid amount. CO-22 marks it as a contractual obligation, while PR-22 marks it as patient responsibility. However, PR-22 doesn’t automatically mean you can bill the patient. Check the coverage and actual patient responsibility first.

Who updates coordination of benefits?

The patient or policyholder usually needs to contact their insurance company to update coordination of benefits information. For Medicare, the patient can call the Benefits Coordination & Recovery Center (BCRC) at 1-855-798-2627. As a biller, you can help identify what’s wrong and provide supporting information, but the insurer must update its records.

How do I know which insurance is primary?

Check all the insurance plans the patient had on the date of service. Then apply the relevant COB rules. For Medicare, review the Medicare Secondary Payer rules. For commercial insurance, check whether coverage comes through employment, a spouse, or a parent. If you’re still unsure, contact the insurers and confirm which plan should pay first.

What is the birthday rule in coordination of benefits?

The birthday rule determines which parent’s insurance pays first when a dependent child is covered under both parents’ health plans. The parent whose birthday comes earlier in the calendar year generally has the primary plan. Only the month and day matter, not the birth year. Different rules may apply when parents are divorced or separated.

Is Medicaid always secondary?

Medicaid is generally the payer of last resort, meaning other responsible insurance plans usually pay first. However, some services follow special rules. For example, certain preventive services for children may qualify for pay-and-chase, where Medicaid pays the provider first and later seeks payment from the responsible insurer. Check your state’s Medicaid billing requirements before submitting the claim.

What does CO-22 with MA04 mean?

CO-22 with MA04 means the payer may be missing information about the primary insurance. This could be the primary insurer’s details or information about what it paid or adjusted. Check the primary EOB and make sure the required information was included with the secondary claim. Then follow the payer’s instructions to correct or resubmit it.

Does CO-22 stop the timely filing clock?

No. A CO-22 denial doesn’t automatically give you more time to file the claim. Original Medicare generally allows 12 months from the date of service, while other insurers have their own deadlines. Check how much time is left, keep proof of earlier submissions, and contact the payer if the deadline is approaching or has already passed.

Final Thoughts

CO-22 denials can take time to resolve, especially when the problem is with the insurance company’s records rather than the claim itself. You may need the patient to update their COB information before the payer can process the claim.

The best way forward is to confirm which insurance should pay first, correct any outdated information, and follow up before the filing deadline passes.

If CO-22 denials keep delaying payments to your practice, A2Z Medical Billing Services can help. Our denial management services help you identify what’s causing the denials, correct billing issues, and follow up with insurance companies to get claims resolved.