Denial Code 100 (CO-100, PR-100) — Meaning & What to Do
Claim Adjustment Reason Code (CARC)
What denial code 100 means: Payment was made to the patient or another party, not the provider.
What to do about denial code 100: Check whether a payment was sent to you that should go to the provider.
CO-100 vs PR-100 vs OA-100: what the prefix means
| Code on your EOB | What the prefix means | Who typically pays |
|---|---|---|
| CO-100 | Contractual obligation — the provider writes the amount off | Usually not the patient |
| PR-100 | Patient responsibility | The patient |
| OA-100 | Other adjustment | Often another payer or plan |
The prefix tells you who is expected to absorb the amount; the number (100) tells you why.
Seeing denial code 100 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 95The provider billed in a way that doesn't follow the plan's rules.
CARC 101A predetermination (pre-check of benefits) was already given.
CARC 94Payment made was more than the charge, creating a credit.
CARC 102A major medical adjustment was applied.
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 100
What does denial code 100 mean on my EOB?
Payment was made to the patient or another party, not the provider.
What should I do about denial code 100?
Check whether a payment was sent to you that should go to the provider.
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.