Denial Code 121 (CO-121, PR-121) — Meaning & What to Do
Claim Adjustment Reason Code (CARC)
What denial code 121 means: An outstanding balance from a previous period was applied.
What to do about denial code 121: Ask for an itemized history of the previous balance.
CO-121 vs PR-121 vs OA-121: what the prefix means
| Code on your EOB | What the prefix means | Who typically pays |
|---|---|---|
| CO-121 | Contractual obligation — the provider writes the amount off | Usually not the patient |
| PR-121 | Patient responsibility | The patient |
| OA-121 | Other adjustment | Often another payer or plan |
The prefix tells you who is expected to absorb the amount; the number (121) tells you why.
Related codes
CARC 118Charges were reduced for a specific health program requirement.
CARC 122This is a non-covered charge because it's a routine/screening exam.
CARC 117Transportation is only covered to the nearest appropriate facility.
CARC 125The claim was submitted with an error in how it was set up.
Keep reviewing your bill
- Medical Bill vs EOB: What Is the Difference?
- How to Dispute a Medical Bill — Find Billing Errors Before You Pay
Frequently asked questions about Denial code 121
What does denial code 121 mean on my EOB?
An outstanding balance from a previous period was applied.
What should I do about denial code 121?
Ask for an itemized history of the previous balance.
Found this code on your bill or EOB?
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