A denied claim on an EOB is rarely a judgement about whether you needed the care. Far more often it is a paperwork failure — and the reason code tells you which one, if you know how to read it.
Here is a denial that looks alarming and is usually fixable.
Sample EOB — denied claim
| Provider | Lakeside Imaging Center |
| Date of service | July 8, 2026 |
| Service | MRI, lumbar spine without contrast (CPT 72148) |
| Billed amount | $1,850 |
| Allowed amount | $0 ← Claim denied, nothing allowed |
| Plan paid | $0 |
| Denial code | CO-197 ← Precertification / authorisation absent |
| Your responsibility | $0 ← CO = contractual; provider cannot bill you |
What the Code Is Telling You
Denials on an EOB carry standardised reason codes. The prefix matters as much as the number: CO means contractual obligation — the provider absorbs it and cannot bill you. PR means patient responsibility — you owe it.
The sample above is CO-197: authorisation was required and was not obtained. Because it is a CO code, an in-network provider who failed to get the authorisation is not permitted to pass that cost to you. If you receive a bill for it anyway, that bill is the error.
Codes You Will Actually See
- PR-1 — deductible. Not a denial. Your plan is working; your deductible is not met.
- PR-2 — coinsurance. Also not a denial. Your share after the deductible.
- PR-3 — copay. The flat fee for that visit type.
- CO-45 — charge exceeds the allowed amount. In-network, the provider writes this off. Out-of-network, expect a balance bill.
- CO-97 — already included in another service. Bundled into a procedure paid on the same day.
- CO-197 — authorisation absent. The one above. Very often appealable.
Which Denials Are Worth Appealing
Three are worth your time, because they succeed often:
- Missing authorisation when the care was urgent, or when the provider simply failed to file. Retroactive authorisation is frequently granted.
- Coding errors — a diagnosis code that does not support the procedure code. This is fixed by the practice resubmitting, not by you appealing.
- Not medically necessary, when your physician will write a letter explaining why it was. This denial is a judgement call, and judgement calls get overturned.
A denial for a service your plan genuinely excludes is a different matter, and appealing it rarely goes anywhere.
How to Appeal Without Wasting the Attempt
Call the insurer first and ask them to explain the denial in plain language — sometimes it is a data-entry problem they can reprocess on the call, with no appeal needed. If you do appeal, file within your plan's deadline, attach the provider's supporting documentation, and keep the claim number on every page. If the internal appeal fails, you have the right to an external review by an independent reviewer whose decision binds the insurer.
If you are looking at a denial and cannot tell whether it is worth fighting, call (713) 575-9904 and read me the code.