Reviewed Sep 20, 2026 · maintained by Erin Rose · general reference, not legal advice
The ten denials, by what the remit says
Each page gives the reason the code lands on a drug or administration line, the fix (corrected claim or appeal), what to attach, and the appeal windows cited to the CFR. The MUE, NCCI and SAD facts on them are read from the CMS tables, not typed.
| Code | What it means on a drug claim | Usual fix |
|---|---|---|
| CO-97 M15 | A second initial administration code was folded into the one that paid (hydration beside an infusion, a push beside a chemo infusion). | Recode the second service to its add-on (96361, 96366, 96367, 96375) and resubmit as a corrected claim. |
| CO-50 N115 / N386 / M76 | The ICD-10 on the drug line is not on the LCD, article or payer policy for that drug. | Coded wrong: corrected claim with the covered code. Truly off-label: redetermination with the medical-necessity package. |
| CO-151 N362 | The units on a J-code or administration line exceed the Medically Unlikely Edit. | Recompute units from the HCPCS billing unit; split by vial or date only when the MUE is claim-line (MAI 1). |
| CO-4 | A single-dose drug line went out without JW or JZ, or with the wrong one. | JZ on the line when nothing was discarded; two lines with JW on the discarded units when something was. |
| CO-16 M119 / M123 | The NDC on the drug line is missing, not 11 digits, deactivated, or has the wrong quantity/unit. | Rebuild the 11-digit NDC with the zero in the short segment, fix quantity and unit of measure, resubmit. |
| CO-197 N54 | No authorization on file (197), or the claim went past the one on file (198): units, dates, dose, site or diagnosis. | Amend the auth to match the claim, or file the retro-authorization request inside the payer’s window. |
| CO-B15 | An add-on administration code (96366, 96367, 96375, 96415, 96417) has no payable initial code on the same claim and date. | Put the add-on and its initial code on one corrected claim; fix the initial line’s denial first if it had one. |
| CO-18 M86 | The payer sees the drug or administration line as an exact duplicate of one it already has. | Recode the second administration, put JW on the discarded-drug line, or resend the correction as frequency 7 with the original claim number. |
| CO-96 | The drug is on your MAC’s self-administered drug list for the route given, so Part B does not pay for it. | IV route: corrected claim with JA. Otherwise bill the line with GY so it denies to the patient, and route future doses through Part D. |
| CO-236 | Two administration codes on the claim are an NCCI column-1/column-2 pair the payer will not pay together as billed. | XU, XS or XE on the column-2 line when the second service was distinct; drop the line when it was part of the primary. |
The appeal ladder
Medicare Part B (five levels; the first three and their windows, cited so you can check them):
- Redetermination by the MAC — within 120 days of the initial determination (42 CFR §405.942).
- Reconsideration by the QIC — within 180 days of the redetermination (42 CFR §405.962).
- ALJ hearing — within 60 days of the reconsideration (42 CFR §405.1014).
Commercial and Medicare Advantage: the payer's reconsideration, then its formal appeal, on the contract's timelines (typically 60–180 days from the remit). A fully-insured plan can be escalated to the state insurance department; a self-funded plan cannot — how to tell which you have. A denial the practice caused (units, modifier, NDC) is a corrected claim, not an appeal, on every payer.
The edits themselves are public: CMS NCCI PTP and MUE tables, updated quarterly, are what every page here reads.
Triage in thirty seconds
- Group code first. CO means the practice eats it unless it fixes the claim; PR means the patient owes it; OA is neither. All ten denials here arrive as CO; the same code under PR (a signed ABN, for instance) moves the amount to the patient.
- Corrected claim or appeal? Units, modifiers, NDC format, duplicate lines, add-on without primary, second initial code: corrected claim (frequency 7), never an appeal. Diagnosis off the policy, SAD, no authorization: appeal or route elsewhere.
- Read the remark code. The CARC is the category; the RARC (M/N code) is the specific reason. M119 and N362 each point to one field on one line.
- Plan type before state law. Prompt-pay interest and recoupment limits reach fully-insured plans only — confirm before you cite them.
Frequently asked
- What is the difference between a CARC and a RARC?
- The CARC (CO-97, CO-151) is the adjustment category on the 835; the RARC (M15, N362) is the remark that narrows it to a specific reason. A denial page here is organized by CARC and names the RARCs that usually ride with it.
- When is a denial a corrected claim rather than an appeal?
- When the practice can change the claim to make it true: units, modifiers, NDC format, codes, pointers, frequency code. An appeal argues the payer was wrong about a true claim — medical necessity, coverage, authorization. Sending an appeal for a units error wastes the window.
- Does CO mean the patient cannot be billed?
- Yes. Contractual-obligation adjustments are the provider's to absorb or fix. Only a PR (patient responsibility) adjustment, or a signed ABN on a Medicare non-covered service billed with GA, moves the amount to the patient.
Related references
Catch the denial before the claim goes out
Claim Check runs every edit on this page — NCCI pairs, MUE, JW/JZ, add-on parents — on the drug and administration lines before you submit, and prices each line at your payer’s published rate.
Open Claim CheckSources & how this is maintained
- What this library is
- Ten denial codes chosen because they are the ones that land on drug and administration lines, written as reason → fix → appeal. Not a dictionary of all 300+ CARCs.
- Sources
- X12 CARC/RARC lists (11/1/2025); CMS NCCI PTP and MUE tables (Q3 2026); MAC SAD exclusion articles; 42 CFR Part 405 Subpart I for the appeal windows.
- Corrections
- Send one with the remit line.