What Are Claim Adjustment Reason Codes (CARCs)?

Claim Adjustment Reason Codes (CARCs) are standardized codes used by health insurance payers to explain why a medical claim or individual service was paid differently than the amount billed. These codes help healthcare providers, medical billers and revenue cycle management teams understand payment reductions, denied services, patient responsibility and other financial adjustments.

CARCs are an important part of the Electronic Remittance Advice (ERA), which is commonly transmitted using the X12 835 Health Care Claim Payment/Advice transaction.

In this guide, we'll explain how CARCs work, how they relate to Claim Adjustment Group Codes and Remittance Advice Remark Codes (RARCs), where they're reported in the X12 835 version 5010 transaction, and how to interpret common adjustment scenarios.

Why Are Claim Adjustment Reason Codes Used?

When a healthcare payer processes a claim, it compares the submitted charges against applicable benefits, coverage requirements, payment rules and other adjudication criteria.

The amount paid may differ from the original billed amount for several reasons. For example, the payer may apply a negotiated contractual allowance, assign part of the allowed amount to a deductible, deny an individual service or make another permitted adjustment.

CARCs provide standardized reasons for these adjustments so that providers and billing systems can interpret remittance information consistently.

For medical billers, CARCs help identify what happened during adjudication and what additional investigation may be necessary. For EDI developers, they provide structured adjustment information that can be associated with specific claims and service lines.

However, the same CARC can appear across different payers and claim scenarios. The code identifies an adjustment reason but does not necessarily explain every detail of the payer's decision or establish the correct follow-up action.

How CARCs Work with Claim Adjustment Group Codes

CARCs are reported together with Claim Adjustment Group Codes, which identify the general financial responsibility category associated with an adjustment.

When viewing an ERA or a payment posting report, these values are often displayed together as combinations such as CO-45, PR-1 or OA-18.

The letters represent the adjustment group code, while the number or alphanumeric value represents the CARC.

For example, CO-45 generally identifies an adjustment related to charges exceeding an applicable payment allowance, while PR-1 identifies a deductible amount assigned to patient responsibility.

Although billing systems may display these values as a single code, they are transmitted separately in the X12 835 transaction.

Important: The adjustment group code is significant when evaluating financial responsibility. However, the group code and CARC alone do not override provider contracts, coverage rules or applicable patient billing restrictions.

Where Are CARCs Located in the X12 835 Version 5010?

In the X12 835 version 5010 transaction, CARCs are reported in the CAS (Claim Adjustment) segment.

The CAS segment may appear at two different levels:

• Loop 2100: Reports applicable claim-level adjustments.
• Loop 2110: Reports applicable service-line adjustments.

Each CAS segment identifies an adjustment group code, one or more reason codes and their associated adjustment amounts. Adjustment quantities may also be reported when applicable.

A single CAS segment can contain multiple reason-code and adjustment-amount combinations that share the same group code. Additional combinations follow the same repeating pattern.

Multiple CAS segments may also be reported when different adjustment groups or additional adjustment information are needed.

For EDI developers, it is important to preserve the relationship between the adjustment group, each individual CARC and its associated amount. These elements should not be interpreted independently.

Example: Reading CARCs in an X12 835 Service-Line Adjustment

Consider a professional claim where a healthcare provider bills $150 for an office visit. During adjudication, the payer allows $110 of the billed charge, resulting in a $40 contractual adjustment. Of the $110 allowed amount, $20 is applied toward the patient's deductible, and the payer pays the remaining $90.

The following simplified service-level X12 835 segments demonstrate how the payer reports these adjustments using Claim Adjustment Reason Codes (CARCs):

Example: Contractual Adjustment and Patient Deductible

Illustrative example only. This is a partial X12 835 transaction using fictional payment information and does not represent a complete interchange or a specific payer's adjudication decision.

Understanding the Example

In this example, the $150 billed charge is accounted for by a $90 payer payment, a $40 contractual adjustment and a $20 deductible assigned to patient responsibility.

The presence of these adjustments does not mean that the service was denied. Instead, they explain how the billed amount was processed and divided among payment, contractual adjustment and patient responsibility.

Actual patient billing must still follow applicable coverage rules, provider agreements and other legal requirements.

Common Claim Adjustment Reason Code Examples

CARCs cover a wide range of adjudication situations. Some describe ordinary financial adjustments, while others relate to coverage limitations, missing information, duplicate claims or denied services.

The following examples represent adjustment codes that medical billing professionals may encounter. They are not a statistical ranking of the most frequently reported CARCs and do not represent the complete X12 code list.

These descriptions summarize common adjustment concepts for educational purposes. Readers should consult the official X12 definitions for the complete code text, usage instructions and current status.

Some codes have specific reporting restrictions. For example, CARC 18 is generally reported with adjustment group OA, except where applicable state workers' compensation requirements call for CO. Similarly, CARC 16 requires additional remark information to help identify the underlying issue.

The official code list is available from X12 Claim Adjustment Reason Codes.

How CARCs and RARCs Work Together

A CARC communicates the reason for a financial adjustment, but it may not provide enough information to identify the exact problem with the claim.

Remittance Advice Remark Codes (RARCs) can provide additional explanation or other important remittance information.

For example, CARC 16 identifies a missing-information or billing-error situation and requires an accompanying remark code. The additional remark information helps narrow down what should be investigated.

In an X12 835 version 5010 transaction, CARCs are reported in the CAS segment, while applicable RARCs may appear in the MIA or MOA segments in Loop 2100, or the LQ segment in Loop 2110.

Medical billers and EDI professionals should evaluate the CARC, adjustment group, associated amount, applicable RARCs and other relevant information reported throughout the X12 835 transaction. This may include the claim status and payment information in the CLP segment, service-level information in the SVC segment, and other applicable remittance details. A CARC should not be interpreted in isolation, as the complete remittance information and payer-specific requirements may be necessary to understand the adjustment and determine the appropriate action.

We'll explore RARCs in greater detail in the next article in this series.

Can Multiple CARCs Be Reported for the Same Service?

Yes. A payer may report multiple financial adjustments against a single service, and each adjustment may have a different reason.

For example, a service may have a contractual adjustment and a separate deductible or coinsurance amount. These adjustments can be reported in separate CAS segments when they belong to different adjustment groups.

Multiple reason codes that share the same group code can also be included within one CAS segment.

Example: Multiple CARCs Within a Single CAS Segment

Consider a medical claim where the payer determines that the patient is responsible for a $20 deductible and an additional $10 in coinsurance. Although both amounts represent patient responsibility, they have different adjustment reasons and are reported using separate CARCs.

The following simplified X12 835 example demonstrates how both adjustments can be reported within a single CAS segment:

This example reports two adjustments under the same PR (Patient Responsibility) group code:

• PR-1 (Deductible Amount): The payer assigns $20 toward the patient's deductible. The CARC is reported in CAS02, with the $20 adjustment amount in CAS03.
• PR-2 (Coinsurance Amount): The payer assigns an additional $10 as the patient's coinsurance responsibility. The CARC is reported in CAS05, with the $10 adjustment amount in CAS06.

The empty CAS04 position indicates that no adjustment quantity is supplied for the first adjustment. The second CARC and its associated amount follow in the next available positions.

In this example, the payer reports a total of $30 in patient responsibility, consisting of a $20 deductible and $10 coinsurance. These amounts represent the patient's portion of the adjudicated service, but do not indicate whether the patient has already paid them. Actual patient billing remains subject to applicable coverage rules, provider agreements and other requirements.

For EDI developers, this example illustrates why each CARC must remain associated with its corresponding adjustment amount. Although both adjustments share the same PR group code, they represent different reasons and should be recorded separately when processing the remittance information.

Claim-Level CARCs vs. Service-Level CARCs

CARCs may apply to an entire claim or to individual service lines. The adjustment's position within the 835 is important when interpreting how the payer processed the claim.

For example, a claim containing several billed services may have one service reduced because of a contractual allowance while another service is denied for medical necessity.

When reviewing service-level adjustments, the billing system should associate each CAS segment with the applicable SVC service line.

Claim-level and service-level adjustments should not be combined without considering their reporting level. An adjustment already reported at the service level should not be counted a second time as a claim-level adjustment.

How Medical Billers Should Interpret a CARC

Identifying the CARC is only the first step in determining what happened during claim adjudication.

Step 1: Identify the Adjustment Group

Determine whether the adjustment is reported as CO, PR, OA or PI. This establishes the general adjustment category and provides context for the associated reason code.

Step 2: Review the CARC and Adjustment Amount

Identify the CARC and its associated adjustment amount, then review the applicable claim or service payment information to understand how the adjustment affects the overall adjudication. Determine whether the adjustment relates to routine payment processing, patient cost sharing, a reduced payment or a potentially denied service.

Step 3: Check for Associated RARCs

Review any applicable remark codes and payer explanations. Additional information may be required to understand the specific cause, particularly when the CARC describes a broad billing issue.

Step 4: Review the Original Claim and Payer Requirements

Compare the adjudication information against the original claim submission, relevant eligibility or authorization records, coding information and applicable payer policies.

Focus on the fields and documentation most closely related to the reported adjustment reason.

Step 5: Determine Whether Follow-Up Is Necessary

Not every CARC requires corrective action. A properly applied contractual adjustment or deductible may only require accurate payment posting.

However, when the payer has denied a service or made an adjustment that appears incorrect, further investigation may be needed.

Depending on the circumstances, the appropriate follow-up may involve a claim inquiry, corrected claim, reconsideration, submission of documentation or a formal appeal.

Always verify the payer's current requirements before taking action. Resubmitting a previously adjudicated claim without identifying the underlying problem may create duplicate processing issues.

Medicare, Medicaid and Commercial Payer Considerations

CARCs are standardized across healthcare remittance transactions, but payers may apply different coverage policies, payment rules and claim review procedures. As a result, the same CARC may be reported by multiple payers for similar adjustment reasons, while the underlying circumstances and appropriate follow-up actions may differ.

Medicare

Original Medicare contractors report claim adjudication information through remittance advice using standardized adjustment codes. The applicable Medicare Administrative Contractor (MAC) can provide guidance on payment policies, claim corrections, reopenings and redeterminations.

Medicare Advantage plans may have different operational and appeal procedures from Original Medicare.

Medicaid

Medicaid fee-for-service programs and Medicaid managed care plans may have different coverage rules, provider billing requirements and denial resolution procedures. State-specific requirements should be reviewed when investigating an adjustment.

Commercial Payers

Commercial payers, including Blue Cross Blue Shield plans and other health insurers, use standardized remittance information while applying their own benefit plans, provider contracts and payment policies.

A CARC may identify the general reason for an adjustment, but the applicable provider agreement or payer policy may be needed to understand why the adjustment was made.

Clearinghouses and Billing Systems

Clearinghouses and electronic payment platforms, including services such as Availity and Office Ally, may make ERA information available through downloadable X12 835 files, readable reports or other supported software integrations.

Billing applications may translate adjustment codes into descriptive messages, but the original code, group, adjustment amount and reporting level should be retained whenever possible.

This helps medical billing and EDI teams investigate disputed adjustments and reconcile payer payments accurately.

Why CARCs Are Important for Payment Posting and Denial Management

Accurate CARC interpretation is valuable for both routine payment posting and denial management.

For example, a payment posting application may use adjustment information to distinguish contractual reductions from patient-responsibility amounts. A denial management system may use CARCs and associated remarks to help identify claims requiring additional review.

Healthcare organizations can also analyze adjustment patterns over time to identify repeated problems involving filing deadlines, authorizations, coding, eligibility or other billing processes.

However, reporting and automation should consider the complete adjustment information rather than relying on CARCs alone. A single code may appear across different claim scenarios, and some adjustments do not represent denials.

Preserving the original X12 835 data can also help EDI teams troubleshoot mapping problems, missing adjustment details and discrepancies between payer remittance information and billing system balances.

Frequently Asked Questions About CARCs

Key Takeaway

Claim Adjustment Reason Codes (CARCs) explain why a payer adjusted a medical claim or service from its submitted billed amount. They are used for both denied services and routine payment adjustments, including contractual allowances and patient cost sharing.

In the X12 835 version 5010 transaction, CARCs are reported in the CAS segment at the claim level in Loop 2100 or the service level in Loop 2110. These codes must be interpreted in the context of the adjustment group, associated amounts, applicable RARCs, claim and service payment information, and other relevant details reported in the remittance advice.

For medical billers and EDI professionals, understanding the complete adjudication information is essential for accurate payment posting, identifying potential denial causes and determining whether additional investigation is necessary. Although CARCs are standardized, payer coverage policies, payment rules and resolution procedures may differ. Always consider the applicable payer's requirements before determining the appropriate follow-up action.

Related Eclaims Articles and Resources

• Medical Claim Denials: Common Reasons Claims Are Denied
• Duplicate Medical Claim Denials
• Rejected Claim vs. Denied Claim

Disclaimer: This article provides general educational information about medical claim adjustments, remittance advice and electronic healthcare transactions. It does not replace official payer instructions, provider contracts, X12 implementation guides or applicable laws and regulations. Code definitions, usage requirements and claim processing policies may change. Always verify current requirements with the appropriate payer or official standards organization.