CO-31 means “Patient cannot be identified as our insured.”
It is a Claim Adjustment Reason Code (CARC) used by payers to explain why a claim was not paid as submitted. The current X12 code list defines CARC 31 with this exact meaning.
In simple terms, the insurance company received the claim but could not match the patient to one of its members. This type of CO-31 denial does not always mean that the patient had no insurance.
The patient may have active coverage, but something on the claim may not match the information held by the insurance company. For example, the member ID may be wrong, the patient’s name may be different, or the wrong insurance plan may have been billed.
That is why a CO-31 denial should be investigated carefully before the claim is simply resubmitted.
The most common reason is incorrect or outdated insurance information i.e
And differences between provider and payer records can all lead to CO-31 denial
For example, a patient may give the provider an insurance card with a member ID that was entered incorrectly during registration. One wrong letter or number can prevent the payer from identifying the patient.
The same thing can happen when the patient’s name or date of birth in the provider’s system does not match the payer’s records.
Another common problem occurs when the patient is covered under a parent’s or spouse’s insurance. In that situation, the patient is not the subscriber. If the billing system incorrectly lists the patient as the subscriber, the payer may not be able to match the claim correctly.
CO-31 denial can also occur when the provider sends the claim to the wrong insurance company or uses an old insurance plan after the patient has changed coverage.
This is why insurance verification is so important before claim submission.
Not exactly.
This is an important point because some online denial code charts describe CO-31 simply as a name and ID mismatch.
The official X12 definition is broader:
Patient cannot be identified as the payer’s insured.
A name or member ID mismatch can cause this problem, but it is only one possible reason.
The billing team should therefore look at the entire insurance record instead of changing only one piece of information.
Consider a patient named Robert Johnson.
The provider submits the claim using the correct insurance company but enters the member ID as AB1234567 instead of AB1234568.
The patient’s coverage may be active. However, the payer cannot find that member ID in its records.
The claim may then receive CO-31 denial.
Here is another example.
A patient has recently changed her last name, but the insurance company still has her previous name in its system. The provider submits the claim using the new name.
The payer may not be able to match the patient correctly.
There can also be a subscriber issue.
Suppose a child is receiving care under the father’s insurance plan. The father is the subscriber, while the child is the dependent. If the claim is submitted with incorrect subscriber information, the payer may be unable to identify the patient correctly.
In all three cases, the patient may actually have valid insurance. The problem is that the information on the claim does not match the payer’s records.
The first step is to understand exactly what the payer is rejecting.
Start with the ERA or EOB and review the claim information. Do not look only at the CO-31 code. Check any accompanying remark code or payer message because it may provide additional information about the problem.
Next, compare the information on the submitted claim with the patient’s insurance information.
Check the patient’s name, date of birth, member ID, subscriber information, relationship to subscriber, group number, and payer.
Then verify the patient’s insurance for the actual date of service.
This is important because a patient who is insured today may not have had the same coverage on the date when the service was provided.
If the eligibility response shows different information, correct the patient’s account first. After that, correct the claim and follow the payer’s process for resubmission.
The important rule is "Do not simply rebill the same claim with the same information. Find and correct the original problem first".
This is where CO-31 denial can become more complicated.
Sometimes the provider’s information is correct, but the payer’s records are incomplete or outdated.
For example, a patient may have recently enrolled in a plan, changed their name, or changed coverage. The payer may not yet have updated its system.
In such cases, the provider should document the eligibility information and contact the payer when necessary.
If the payer confirms that the patient was covered on the date of service, the claim may need to be corrected, resubmitted, or disputed according to that payer’s rules.
The key is to determine whether the problem came from the provider's information or the payer's records.
Medicare claims require special attention to patient identification.
Medicare uses the Medicare Beneficiary Identifier (MBI) for Medicare transactions. CMS states that providers must use the MBI for Medicare claims, subject to limited exceptions. CMS also states that the MBI is confidential information and should be protected.
Therefore, when a Medicare claim has a patient identification problem, the billing team should carefully check the beneficiary’s MBI and other identifying information.
CMS also provides the HIPAA Eligibility Transaction System (HETS), which allows authorized users to check Medicare eligibility information in real time through the standard 270/271 eligibility transaction.
This can help the billing team confirm whether the patient’s Medicare information is correct before the claim is resubmitted.
The best way to reduce CO-31 denial is to catch the problem before the claim is submitted.
The process should begin when the patient schedules an appointment or registers with the practice.
The practice should collect the patient’s current insurance information and verify it before billing. Returning patients should also have their insurance information reviewed because coverage can change between visits.
Eligibility verification should be performed for the appropriate date of service rather than relying only on an old insurance card.
The billing team should also make sure that the patient and subscriber information are entered correctly. This is especially important when a child, spouse, or other dependent is covered under someone else’s insurance.
A good front end process can prevent many CO-31 problems before they ever reach the claims department.
When CO-31 denial appears, the RCM specialist should think through the claim in a logical order
Is this the correct patient?
Then:
Is this the correct insurance?
Then:
Is this the correct member ID and subscriber information?
Then:
Was the coverage active on the date of service?
Finally:
Does the information match the payer’s records?
This simple approach helps the billing team find the real cause instead of repeatedly resubmitting the claim.
CO-31 denial does not simply mean that a patient has no insurance.
It means the payer cannot identify the patient as its insured based on the information associated with the claim.
The problem may be an incorrect member ID, patient information, subscriber information, payer selection, outdated insurance information, or a difference between the provider’s records and the payer’s records.
The best solution is not to keep rebilling.
Verify the information, find the mismatch, correct the patient record, correct the claim, and then resubmit according to the payer’s rules.
More importantly, practices should use CO-31 denials to identify problems in their registration and eligibility process. If the same error keeps happening, the real solution is to fix the process that is creating the denial.
Disclaimer: This article is provided for general educational and informational purposes only. The examples and information used are fictional or generalized and do not relate to any real patient or patient's medical, insurance, or billing information. Payer policies, requirements, and denial code usage may vary and can change over time. Always verify current payer guidelines and applicable official requirements before taking action on a claim.
CO-31 means the patient cannot be identified as the payer's insured. In simple terms, the insurance company received the claim but could not match the patient on the claim to one of its members. This does not always mean that the patient had no insurance.
The patient may have active coverage, but something on the claim may not match the information held by the insurance company. For example, the member ID may be wrong, the patient's name, patient date of birth may be different, may be wrong subscriber information or the wrong insurance plan may have been billed.
It is usually related to patient or insurance identification. CO-31 means the patient cannot be identified as the payer's insured. However, the exact reason should be determined by checking the claim, insurance and eligibility information, and payer response.
Incorrect member ID, incorrect patient information, wrong subscriber information, wrong payer, outdated insurance information, and differences between provider and payer records can all lead to CO-31.
Verify the patient's insurance for the date of service, compare the information with the payer's records, correct the underlying information, and resubmit or otherwise resolve the claim according to payer requirements.
No. A member ID mismatch can cause CO-31, but CO-31 has a broader meaning, the payer cannot identify the patient as it's insured.
In simple terms, the insurance company received the claim but could not match the patient on the claim to one of its members. The patient may have active coverage, but something on the claim may not match the information held by the insurance company. For example, the member ID may be wrong, the patient's name may be different, or the wrong insurance plan may have been billed. That is why CO-31 should be investigated carefully before the claim is simply resubmitted.
Yes. Accurate registration with updated and correct patient information, regular insurance verification, correct subscriber information, and proper eligibility checks can help prevent CO-31.
Not automatically. The practice should first determine why the denial occurred and whether the balance is actually the patient's responsibility.
