CO 24 denial code

What CO-24 means

CO-24 means the payer you billed does not hold the patient’s benefits for this service: those charges belong to a capitation arrangement or managed care plan. In everyday Part B billing, the overwhelmingly common scenario is a patient enrolled in a Medicare Advantage plan whose claim was sent to traditional Medicare. Original Medicare sees the enrollment on file and denies, because the MA plan administers the patient’s Part A and Part B benefits.

The CO group code means contractual obligation: you cannot bill the patient for the denied amount. The denial is directional, not final; the service may be perfectly payable, just by a different payer.

Capitation is the other flavor. If your group is paid a fixed per-member-per-month amount under a capitated contract, fee-for-service claims for covered members deny with CO-24 because the capitation payment already covers the service.

Common causes

• Medicare Advantage enrollment missed at intake. Patients often present the red-white-and-blue Medicare card even after enrolling in an MA plan, and the front desk registers traditional Medicare.
• Mid-year plan changes. The patient joined an MA plan during an enrollment period after their registration record was built, so old payer data rode along on new claims.
• Capitated services billed fee-for-service. The service falls inside your capitation agreement, and the plan will not pay it separately.
• Hospice or other managed arrangements holding the benefit for the billed service, depending on the payer’s setup.

How to fix and resubmit

1. Run eligibility for the date of service through your MAC portal or clearinghouse. The response shows whether the patient was enrolled in an MA plan on that date and which one. Noridian’s guidance for this denial is exactly that: verify eligibility, then bill the plan listed.
2. Get the plan’s billing details: payer ID, claims address, and the patient’s member ID from their plan card. The MA member ID is not the Medicare Beneficiary Identifier.
3. Rebill the claim to the MA plan as a new claim. This is not a corrected claim or an appeal to Medicare; Medicare adjudicated correctly. Do not appeal the CO-24 unless eligibility shows the patient was not actually enrolled in a plan on the date of service.
4. Check the MA plan’s timely filing limit immediately. Plan limits are often shorter than Medicare’s 12 months: 90 days to 180 days is common. If the misdirected claim burned most of the window, submit to the plan the same week and keep proof of the original submission date in case you need a filing-limit exception. If the window has already closed, see CO-29 for how filing-limit exceptions work.
5. If the denial stems from your own capitation agreement, confirm whether the service is inside or outside the cap. Carve-out services can be billed fee-for-service; capitated ones are covered by the monthly payment and should be closed without rebilling.

How to prevent it

Verify eligibility for every Medicare patient at every visit, not just new patients. MA enrollment can change during annual and special enrollment periods, and the eligibility response is the only reliable source. Train front-desk staff that the traditional Medicare card does not prove traditional Medicare coverage; ask specifically about Advantage plans and scan both cards. For capitated contracts, keep an updated list of carved-out services at charge entry. Compare with CO-22, where coordination of benefits points to a different payer, and see the denial codes index for more.