CO-24 means the payer believes the service is already paid for under a capitation agreement or managed care plan, so it will not pay the claim you sent; in Medicare billing it almost always means the patient was in a Medicare Advantage plan on the date of service.
CARC 24 is one of the most fixable denials on a remittance. The service is rarely the problem. The claim simply went to the wrong place, or it went to the right place without the modifier that tells the payer why it should pay.
The fix depends on who sent the code. A Medicare Administrative Contractor (MAC) uses CO-24 when its records show a Medicare Advantage (MA) enrollment. A commercial HMO or Medicaid managed care plan uses it when the service is covered by a capitation payment that a primary care practice or medical group already receives each month.
This guide explains the official wording, the real causes behind each version, how to resolve each one, and the front-desk checks that stop CO-24 before a claim is ever sent.
Key Takeaways
- The official CARC 24 text reads: Charges are covered under a capitation agreement/managed care plan.
- From a Medicare contractor, CO-24 usually means the patient was enrolled in a Medicare Advantage plan on the date of service, so the MA plan, not Original Medicare, should be billed.
- Original Medicare still pays some claims for MA enrollees: hospice-related attending physician care and care unrelated to the terminal illness (modifiers GV and GW), and qualifying clinical trial services (Q0 and Q1).
- First Coast (FCSO) notes that claims returned as unprocessable cannot be appealed; you correct and resubmit, or ask for a reopening when the enrollment record was wrong.
- The CO group code makes the amount a contractual obligation, so do not transfer it to the patient.
What the CO-24 Denial Code Means
Every remittance adjustment has two parts: a group code that says who is responsible, and a Claim Adjustment Reason Code (CARC) that says why. X12, which maintains the code list, defines both pieces as follows.
| Element | Official meaning | What it tells your team |
|---|---|---|
| CO | Contractual Obligation | The provider is responsible for the adjustment; it is not a patient balance |
| CARC 24 | Charges are covered under a capitation agreement/managed care plan | Another arrangement is responsible for paying this service |
| Typical source | Medicare MAC, commercial HMO, Medicaid managed care plan | The fix differs by payer type, so read who issued it first |
CO-24 is not a coding judgment. The payer is not saying the CPT code, diagnosis or documentation was wrong. It is saying that, according to its enrollment or contract records, someone else should pay. That is why the first step is always eligibility, not recoding.
Why Medicare Returns CO-24
Noridian’s reason code guidance lists four situations behind a Medicare CO-24. Each one has a different fix, so identify which applies before you touch the claim.
1. Active Medicare Advantage enrollment. The patient was in an MA plan on the date of service. MA replaces Original Medicare for most services, so the claim belongs to the MA plan.
2. Disenrollment not yet on file. The patient left the MA plan, but the Common Working File (CWF) has not been updated. Medicare still thinks the plan is active.
3. MA enrollee who elected hospice. Original Medicare covers the attending physician’s services and care unrelated to the terminal illness, but the claim needs modifier GV or GW to show that.
4. MA enrollee in a qualifying clinical trial. Original Medicare covers routine costs of qualifying clinical trials, which requires modifier Q0 or Q1 on the line.
First Coast adds a fifth case for dialysis: when a patient with end-stage renal disease is covered under a capitation arrangement, check eligibility and contact the capitation provider before the service is given. For patients with other coverage on top of Medicare, the order of payment follows the rules in our Medicare Secondary Payer guide.
Medicare modifiers that resolve CO-24
| Modifier | Meaning | When to use it |
|---|---|---|
| GV | Attending physician not employed or paid under agreement by the patient’s hospice provider | MA enrollee on hospice, billed by the attending physician |
| GW | Service not related to the hospice patient’s terminal condition | MA enrollee on hospice, care for an unrelated problem |
| Q0 | Investigational clinical service provided in a clinical research study that is in an approved clinical research study | Investigational item or service in a qualifying trial |
| Q1 | Routine clinical service provided in a clinical research study that is in an approved clinical research study | Routine costs in a qualifying trial |
Why Commercial and Medicaid Plans Return CO-24
Outside Medicare, CO-24 usually comes from a capitated arrangement. Under capitation, a payer pays a primary care practice, medical group or delegated vendor a fixed amount per member per month for a defined list of services. Anything on that list is not paid again as fee-for-service.
- The service is in your own capitation. A capitated primary care office bills a routine visit that is already covered by its monthly payment. The claim is an encounter record, not a payment request.
- The service is carved out to a vendor. Lab, imaging, behavioral health or therapy may be capitated to a separate company, so the health plan sends you to that vendor instead.
- The patient is assigned to another provider. In some HMO and Medicaid managed care plans, the member is assigned to a specific primary care provider or group, and services billed by others are denied or redirected.
- The contract changed. The capitation list or carve-outs were updated at renewal, but your billing rules were not.
For these denials, your payer contract is the deciding document. If the service is not on the capitation list in your agreement, ask the payer to reprocess and cite the contract page. Our guide to contractual adjustments in medical billing explains how to post the write-off correctly when the denial is valid.
How to Fix a CO-24 Denial
- Read who issued it. Note the payer, the date of service and any remark codes. A Medicare CO-24 and a commercial CO-24 are worked differently.
- Check eligibility for the date of service. Use your MAC’s portal (for example the Noridian Medicare Portal or First Coast’s SPOT) or a HETS-based eligibility check to see whether an MA plan was active on that exact date.
- If an MA plan was active, bill the MA plan. Get the plan name, member ID and payer ID, confirm your network status and any authorization rules, and submit a new claim to the plan within its filing limit.
- If the MA plan was not active, ask Medicare to reprocess. Once CMS records show no MA enrollment on the date of service, resubmit the claim. If the timely filing window has passed, request a reopening instead.
- If hospice or a clinical trial applies, add the modifier. Rebill with GV, GW, Q0 or Q1 as appropriate, or request a reopening with the modifier if the filing limit has expired.
- For commercial or Medicaid plans, check the contract. Confirm whether the service is in your capitation, carved out to a vendor or tied to an assigned provider, then rebill the right entity or dispute with the contract language.
- Fix the registration record. Update the patient’s insurance on file so the next visit does not repeat the denial.
Do not file a formal appeal for a returned Medicare CO-24 claim. First Coast states that claims returned as unprocessable cannot be appealed. Correct the payer or modifier and resubmit, or request a reopening if the time limit has passed.
A denial that needs a different payer is closer to a rejection than a clinical dispute. Our article on denied vs rejected claims explains why the workflow differs, and our medical claim appeal process guide covers the cases where a formal appeal is the right route.
Worked Example: A Patient Who Switched to Medicare Advantage
Here is a hypothetical but common scenario.
| Stage | What happened |
|---|---|
| Registration | A returning patient shows the red, white and blue Medicare card that is already on file. Nobody asks about plan changes. |
| Claim | The office visit is billed to the Part B MAC. |
| Remittance | The line comes back with group code CO and CARC 24. |
| Eligibility check | The MAC portal shows the patient joined an MA plan during open enrollment, effective January 1. |
| Resolution | The biller gets the MA plan card, confirms the practice is in network, and submits a new claim to the MA plan. |
| Prevention | Registration now asks every Medicare patient whether they changed plans and scans all cards at each visit. |
The rule of thumb. Eligibility on the date of service decides the payer. A card on file from last year does not.
January is the riskiest month. Changes made during Medicare’s annual open enrollment period take effect on January 1, so re-verify every Medicare patient’s coverage at their first visit of the year.
CO-24 vs Similar Denial Codes
Several CARCs point to a payer or coverage problem. Reading the exact code saves time, because each one needs a different fix.
| Code | Official description | Best next step |
|---|---|---|
| CO-24 | Charges are covered under a capitation agreement/managed care plan | Bill the MA plan or capitated entity, or add GV, GW, Q0 or Q1 |
| CO-109 | Claim/service not covered by this payer/contractor. You must send the claim/service to the correct payer/contractor | Find the correct payer or contractor and send it there |
| CO-22 | This care may be covered by another payer per coordination of benefits | Bill the primary payer first, then send the secondary claim |
| CO-27 | Expenses incurred after coverage terminated | Confirm termination date and find the new coverage |
| CO-31 | Patient cannot be identified as our insured | Check member ID, name and date of birth against the card |
| CO-97 | The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated | Review bundling edits and modifiers, not eligibility |
CO-24 and CO-97 are often confused because both say the service is already paid for. The difference is the source: CO-97 points to another claim line or procedure, while CO-24 points to a capitation or managed care arrangement. For a wider view of how these codes fit together, see why medical claims are denied and how to fix them.
How to Prevent CO-24 Denials
Almost every CO-24 can be stopped at the front desk. First Coast’s prevention advice is simple: check eligibility before you bill, ask about new plans, and copy every insurance card.
- Run an eligibility check for every Medicare patient before the visit, not only new patients.
- Ask each patient whether they have joined or left a Medicare Advantage, HMO or Medicaid managed care plan.
- Scan the front and back of every card at each visit, including MA and supplemental plan cards.
- Flag hospice and clinical trial patients in your system so the right modifiers are added at charge entry.
- Keep a current list of capitated services and carve-out vendors for each managed care contract.
- Track CO-24 by payer and location each month to find registration gaps.
Outsourced insurance eligibility verification is often the fastest way to close these gaps when front-desk staff are stretched.
Do not bill the patient for a CO-24 amount. The CO group code assigns it to the provider. Bill the correct payer, or write it off if the service is truly covered by your own capitation.
Seeing CO-24 on more remittances than you should? Steady Medical Billing’s denial management team traces each one to the right payer, rebills it and fixes the registration step that caused it.
Frequently Asked Questions
What does the CO-24 denial code mean?
CO-24 means the charges are covered under a capitation agreement or managed care plan. From Medicare, it usually means the patient was enrolled in a Medicare Advantage plan on the date of service, so the claim must go to that plan.
Can I appeal a CO-24 denial from Medicare?
Usually not. First Coast states that claims returned as unprocessable cannot be appealed. Bill the Medicare Advantage plan, or if Medicare records were wrong or a hospice or clinical trial modifier was missing, resubmit or request a reopening.
Does Original Medicare ever pay for a Medicare Advantage patient?
Yes, in limited cases. For MA enrollees who elected hospice, Original Medicare covers attending physician services and care unrelated to the terminal illness with modifiers GV or GW. It also covers qualifying clinical trial services billed with Q0 or Q1.
Can I bill the patient for a CO-24 denial?
No. The CO group code means contractual obligation, so the amount is not patient responsibility. Send the claim to the correct plan or, if the service is covered by your own capitation, write it off.
What is the difference between CO-24 and CO-109?
CO-24 says the service is covered under a capitation agreement or managed care plan. CO-109 says the payer does not cover the claim and you must send it to the correct payer or contractor. Both require an eligibility check, but CO-24 points specifically to managed care.
