CO-33 denial code
Insured has no dependent coverage
How to fix it
Confirm whether the patient has separate coverage of their own. Otherwise the balance transfers to patient responsibility.
How to prevent it
Verification should return who is covered, not merely that the policy is active.
In practice
A spouse is seen and the claim returns CO-33. The card lists the subscriber's name, the policy is active, and the practice assumed family coverage because the patient presented the card.
The policy is individual. It covers the subscriber and nobody else, and the card gives no visual indication of that — cards are issued to subscribers and rarely enumerate who is actually covered.
The first question is whether the patient has coverage of their own through an employer, a marketplace plan or a public program. Where they do, the claim rebills there. Where they do not, the balance is genuinely theirs and the conversation is better held early than after a second denial.
What sits behind it
This denial reveals a gap in how verification is usually performed. Checking that a policy is active answers a different question from checking that this patient is covered by it, and eligibility responses do return covered dependents where the practice reads that segment rather than stopping at the active flag.
Individual-only policies have become more common as marketplace enrolment has grown, since subsidies are calculated per person and families sometimes enrol members separately across different plans. A household can hold three policies from two carriers with different covered members on each.
Dependent age limits produce the same code at a predictable moment. Coverage to age 26 ends on a date the plan defines — sometimes the birthday, sometimes the end of that month, sometimes the plan year end — and a patient seen just after that boundary looks identical to one who was never covered.
Related codes
Terms used here — Eligibility Verification · Coordination of Benefits · Patient Responsibility
How we handle it — Eligibility Verification · Patient Collections · Denial Management
Primary sources
The rules behind CO-33, at the bodies that publish them.
- Medicare Secondary Payer Manual (opens in a new tab)
Centers for Medicare & Medicaid Services — When Medicare pays second, and to whom the claim goes first. Coordination-of-benefits denials are resolved here rather than with the patient.
- Medicare Coverage Database (LCD/NCD) (opens in a new tab)
Centers for Medicare & Medicaid Services — Searchable national and local coverage determinations. The direct answer to whether a diagnosis supports medical necessity for a given procedure.
- Claim Adjustment Reason Codes (CARC) (opens in a new tab)
X12 — The authoritative, maintained CARC list. Our denial code lookup explains these in plain English; X12 is where the canonical definitions live.
Looking for a different code? Search all 190 CARC and RARC codes
Questions about CO-33
Read the covered-members segment of the eligibility response rather than the active-coverage flag. The response identifies who the policy covers, and a patient who does not appear there will generate this denial no matter how current the card looks.
Yes, and it is one of the more common causes. Coverage ending at age 26 terminates on a date the plan sets, which may be the birthday, the end of that month, or the plan year end. A patient seen shortly after that date is indistinguishable from one never covered.
Once you have confirmed no other coverage applies, generally yes, since no plan contract governs a patient the plan does not cover. Check for a spouse's policy, a marketplace plan or a public program first — patients frequently hold coverage they did not present.
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