Denial Code 4 (CO-4, PR-4) — Meaning & What to Do
Claim Adjustment Reason Code (CARC)
What denial code 4 means: The procedure code doesn't match a required modifier, or the modifier is missing/invalid.
What to do about denial code 4: Ask the provider to review the coding and resubmit the claim correctly.
CO-4 vs PR-4 vs OA-4: what the prefix means
| Code on your EOB | What the prefix means | Who typically pays |
|---|---|---|
| CO-4 | Contractual obligation — the provider writes the amount off | Usually not the patient |
| PR-4 | Patient responsibility | The patient |
| OA-4 | Other adjustment | Often another payer or plan |
The prefix tells you who is expected to absorb the amount; the number (4) tells you why.
Seeing denial code 4 on your EOB?
A denial code tells you what the payer reported, but it may not tell the whole story. Reviewing your EOB and bill together can help clarify what may need attention.
Related codes
CARC 3This amount is your copay — a fixed fee for the visit or service.
CARC 16The claim is missing information or has an error that must be fixed before it can be processed.
CARC 2This amount is your coinsurance — your percentage share of the cost.
CARC 18This looks like a duplicate of a claim already submitted.
Keep reviewing your bill
- Medical Bill vs EOB: What Is the Difference?
- How to Dispute a Medical Bill — Find Billing Errors Before You Pay
- What Is an Itemized Medical Bill? How to Request One
Frequently asked questions about Denial code 4
What does denial code 4 mean on my EOB?
The procedure code doesn't match a required modifier, or the modifier is missing/invalid.
What should I do about denial code 4?
Ask the provider to review the coding and resubmit the claim correctly.
Seeing this code on your own EOB?
Upload the EOB, the bill, or both — MD Bill Check reads the codes on your documents, compares them side by side, and flags what's worth questioning. Free, no account needed.