CARC and RARC Codes: A Complete Reference Guide
Understand CARC and RARC denial codes, how they work together, and what to do about the most common ones. Includes tables of CO, PR, and OA codes with explanations and resolution guidance.
What Are CARC and RARC Codes?
When a payer processes a claim and makes a payment adjustment, they are required to communicate why using a standardized set of codes. CARC codes (Claim Adjustment Reason Codes) and RARC codes (Remittance Advice Remark Codes) are those codes. They appear on the 835 electronic remittance advice transaction, which is what your practice management system receives when a payer adjudicates a claim.
Quick Answer: CARC codes explain why a payment was adjusted or denied. RARC codes provide supplemental detail. Together they form the standard vocabulary of insurance claim denials. Understanding them is fundamental to denial management because the code tells you not just what happened, but what category of problem you are dealing with, and therefore what action you need to take.
The codes are maintained by X12, the standards body that governs electronic healthcare transactions under HIPAA. X12 updates the code sets periodically, so occasionally a code you have seen for years gets modified or a new one is added.
How the Code System Works
Every payment adjustment line on an 835 includes at minimum:
- A group code (who is responsible for the adjustment)
- A CARC code (the reason for the adjustment)
- Optionally, one or more RARC codes (additional context)
Reading these three elements together is what actually tells you what happened and what to do next.
## What Are the Group Codes?
Group codes are often overlooked but they are the first filter. They tell you who bears financial responsibility for the adjustment.
| Group Code | Full Name | Patient Billable? | Meaning |
|---|---|---|---|
| CO | Contractual Obligation | No | Provider write-off per contract or fee schedule. Cannot bill the patient. |
| PR | Patient Responsibility | Yes | Patient owes this amount (deductible, copay, coinsurance). |
| OA | Other Adjustment | Depends | Does not fit CO or PR. Common with COB, secondary claims, and some denials. |
| PI | Payer Initiated Reduction | No | Payer reduced payment unilaterally. Often appealable. |
| CR | Correction/Reversal | No | Adjustment to a previous payment or claim. |
A CO-45 and a PR-45 are completely different situations even though the CARC number is the same. CO-45 is a contractual write-off that you absorb. PR-45 would mean the patient owes the difference. (In practice, you rarely see PR-45; CO-45 is much more common.)
## How CARC and RARC Codes Work Together
The CARC code gives you the primary reason. The RARC code gives you the detail. Some CARC codes are specific enough to act on alone. CO-29 (timely filing expired) is unambiguous. Others are vague by design. CO-16 (claim lacks information) tells you almost nothing on its own; the accompanying RARC code is what tells you what information is actually missing.
When you see CO-16 without a RARC code, it is worth calling the payer. That combination is sometimes used as a generic rejection when the payer's system did not process correctly rather than because something is actually missing from the claim.
Common CARC Codes Reference Table
## CO Group: Contractual Obligation
These are adjustments the provider writes off per their contract or per statute. The patient cannot be billed for CO adjustments unless the code is also accompanied by a PR group.
| Code | Short Name | Description | Typical Cause | Resolution |
|---|---|---|---|---|
| CO-4 | Modifier inconsistent | The procedure code is inconsistent with the modifier used or a required modifier is missing | Modifier applied to wrong code; NCCI edit violation; incorrect modifier selection | Coder review; correct modifier or remove if inappropriate; resubmit |
| CO-16 | Missing/invalid information | Claim/service lacks information or has submission/billing errors | Catch-all denial; missing field; payer system issue | Call payer to identify exactly what is missing; RARC code should specify |
| CO-18 | Duplicate claim | Exact duplicate claim/service | Claim submitted twice; crossover claim already processed; payer system error | Verify original claim status; if different DOS or service, request reprocessing with documentation |
| CO-22 | COB - may be covered by another payer | Payment adjusted because this care may be covered by another payer per coordination of benefits | Other insurance listed as primary; COB information missing or outdated | Verify payer order with patient; update COB; request reprocessing with correct COB information |
| CO-27 | Coverage terminated | Expenses incurred after coverage terminated | Coverage ended before date of service; retroactive termination | Verify coverage dates with payer; check if COBRA or continuation applies; may need to bill patient |
| CO-29 | Timely filing expired | The time limit for filing has expired | Claim filed after payer's filing window; late secondary claim | Appeal with proof of original timely submission (clearinghouse transmission receipt, portal confirmation); win rate is low without documentation |
| CO-45 | Exceeds fee schedule | Charge exceeds fee schedule/maximum allowable or contracted fee arrangement | Billed amount exceeds allowed; contractual adjustment | Standard contractual write-off; generally not appealable; write off per contract |
| CO-50 | Non-covered/medical necessity | These services are non-covered because they are not deemed medically necessary by the payer | Payer criteria not met; experimental or investigational service | Gather clinical documentation; request peer-to-peer review; formal appeal with medical necessity letter |
| CO-97 | Service bundled | Benefit for this service is included in the payment for another service already adjudicated | NCCI bundling edit; component of a more comprehensive code | Coder review of CCI edits; modifier 59 (or XE/XP/XS/XU) if services were truly distinct and separate |
## OA Group: Other Adjustments
OA codes often appear in COB situations, secondary claims, or when the payer is communicating something that does not neatly fit CO or PR. The billing implications depend on the specific situation.
| Code | Short Name | Description | Typical Cause | Resolution |
|---|---|---|---|---|
| OA-23 | Prior adjudication impact | Payment adjusted due to the impact of prior payer(s) adjudication including payments and/or adjustments | Primary payer has already paid; secondary calculation applied | Submit with primary EOB attached; verify secondary billing calculation; may indicate correct processing |
## PR Group: Patient Responsibility
PR codes indicate the patient owes the balance. These are not denials in the revenue recovery sense; they are allocations of financial responsibility to the patient. You collect these from the patient, not from the payer.
| Code | Short Name | Description | Typical Cause | Patient Action |
|---|---|---|---|---|
| PR-1 | Deductible | Deductible amount | Patient has not met annual deductible | Bill patient; verify deductible balance via eligibility inquiry |
| PR-2 | Coinsurance | Coinsurance amount | Standard coinsurance per plan (e.g., 80/20 split) | Bill patient for coinsurance percentage |
| PR-3 | Copayment | Co-payment amount | Standard copay per plan for office visits, specialist visits, etc. | Collect from patient at time of service; if not collected, bill patient |
One practical note on PR codes: if you are seeing a large volume of PR-1 or PR-2 adjustments on claims where the patient was told at the time of service that they had no cost-sharing responsibility, that is usually an eligibility verification problem, not a billing problem. The coverage data on file at the time of service was incorrect.
RARC Codes: The Detail Layer
RARC codes are where the actionable specifics live. They are almost always paired with a CARC code and exist to provide information the CARC code cannot communicate on its own.
## How to Read RARC Codes
There are two main categories of RARC codes:
- MA (Medicare Alert) codes - Information specific to Medicare adjudication; often informational rather than requiring action
- N codes - The main series; covers everything from missing information specifics to appeal rights to benefit limitations
When you receive an 835 with CO-16 and a RARC code, the RARC tells you what is actually missing. Without it, you are guessing. If the RARC code is absent and the payer is using CO-16, a phone call is almost always the fastest path to resolution.
## Common RARC Codes
| Code | Description | Action Required | What to Do |
|---|---|---|---|
| N19 | Procedure code incidental to the primary procedure | No action if correct; appeal if incorrect | Verify if bundling applies; if services were distinct, add modifier and resubmit |
| N20 | Service not payable with other service rendered on the same date | Review coding | Check NCCI edits; if services were medically distinct, modifier may resolve |
| N30 | Missing/incomplete/invalid patient medical record number | Yes | Resubmit with correct medical record number in the appropriate field |
| N56 | Procedure code billed is not correct/valid | Yes | Verify CPT code; consult coder; resubmit with correct code |
| N95 | The amount paid is the maximum for this benefit category for the plan year | No appeal if limit is correct | Communicate to patient; verify benefit limits; document in patient account |
| MA04 | Secondary payment cannot be considered without identity of or payment information from the primary payer | Yes | Submit with primary EOB/remittance; include primary payer ID and payment amount |
| MA130 | Your claim contains incomplete and/or invalid information and no appeal rights are afforded | Yes - urgent | This is a Medicare-specific code; contact Medicare to determine what is deficient; claim must be corrected and resubmitted |
## The Difference Between N and MA Codes
The MA series is specific to Medicare fee-for-service claims processed by Medicare Administrative Contractors (MACs). If you are working a commercial payer claim and see an MA code, that is unusual and worth noting. MA130 in particular is serious: it indicates a claim was returned as unprocessable and there are no appeal rights until the underlying issue is corrected.
N codes apply broadly across payer types, though individual payers may have their own RARC supplements on top of the X12 standard.
How CARC and RARC Codes Work in Practice
## Scenario 1: CO-4 with No RARC
You receive CO-4 (procedure code inconsistent with modifier). No RARC code accompanies it.
The first question is whether the modifier on the claim makes sense with the CPT code. CO-4 is associated with several different situations. Modifier 25 (separate E&M service on same day as procedure) is one of the most common sources. If a provider billed an E&M and a procedure on the same date, payers increasingly require documentation that the E&M was truly separate and distinct. Modifier 59 (distinct procedural service) on a bundled code is another common trigger.
A coder review of the specific CPT/modifier combination against NCCI edits is the right first step. If the modifier was appropriate but missing, add it and resubmit. If it was incorrect, determine the correct modifier or whether the procedure was actually a separate billable service.
## Scenario 2: CO-16 with MA130 (Medicare)
This is an urgent situation. MA130 means Medicare has determined the claim has missing or invalid information and it cannot be processed. There are no appeal rights until it is corrected. The claim must be identified, the deficiency corrected, and a new claim submitted.
Call the MAC if the specific issue is not clear from the 835. These sometimes arise from claim transmission errors that corrupt specific fields.
## Scenario 3: OA-23 on a Secondary Claim
OA-23 on a secondary claim is often not a problem at all. It is communicating that the secondary payment calculation takes into account what the primary payer already paid. If the secondary is processing correctly and the payment you received is what you expected, no action is needed.
If the secondary payment is lower than expected, verify the primary EOB you submitted was complete and accurate. Secondary payers calculate their obligation based on the primary's allowed amount, not the billed amount.
## Scenario 4: CO-29 with No Documentation
Timely filing denials without proof of original submission are the most difficult to recover. Before assuming the claim is a write-off, check:
- Your clearinghouse's transmission report for the original submission date
- Your practice management system's claim history for submission timestamps
- The payer's portal for any record of the original claim
- Whether you have a 277 acknowledgment from the payer (277 CA or 277 U)
If you can produce a 277 acceptance with a date within the payer's filing window, that is usually sufficient for a timely filing appeal. Payers vary in what documentation they will accept. Some will accept clearinghouse reports; others require the actual 277 transaction.
Staying Current on Code Changes
X12 releases code set updates on an annual basis, typically effective January 1. New codes are added, descriptions are revised, and occasionally codes are retired. Payers are not always consistent about adopting updates on the X12 schedule, so a code that appears in the current X12 standard may not yet be in use by all payers.
The practical implication for denial management teams is to review your CARC/RARC reporting periodically for codes that appear in your ERA data but are not in your internal reference. Those may be updated descriptions, newly added codes, or payer-specific codes that fall outside the X12 standard (some payers use non-standard codes on their proprietary remittances).
The X12 code set is publicly available at x12.org and CMS maintains a supplemental RARC list at cms.gov. If a code appears on an ERA and is not in your system, those two sources should be your first lookup.
A Note on Payer-Specific Behavior
One thing the code definitions do not capture is how individual payers actually use these codes in practice. CO-16 is a good example. Technically it means "claim lacks information." In practice, it is used by some payers as a catch-all denial on certain high-dollar claim types that they want additional documentation for, even when the claim is complete as submitted.
Similarly, CO-4 is technically about modifier inconsistency, but a subset of CO-4 denials from certain payers are actually COB issues that got miscoded internally. If you see a pattern of CO-4 from a specific payer and the coding looks correct, it is worth calling to ask what is actually driving the denial before routing to a coder.
The codes are the starting point for understanding a denial. They are not always a complete picture. Experienced denial management teams maintain payer-specific notes on how particular codes manifest with particular payers, because that institutional knowledge changes what action you take and in what order.
Dylan Wilson
Roony