Instantly find explanations, causes, and resolution steps for every Claim Adjustment Reason Code (CARC) and Remark Code.
Claim Adjustment Reason Codes (CARC) explain why a payment differs from what was billed. Every 835 ERA and EOB uses these standardized codes.
Search any code or keyword above. Each page includes the full description, common causes, resolution steps, and appeal guidance.
Each denial code page also links to a dedicated Remark Code page — optimized for providers searching for ERA remark code context.
Most denials are reversible. Our guides walk you through the correct steps to correct, resubmit, or formally appeal each denial type.
| Code | Description | View |
|---|---|---|
| 582 | Denied. | Details → |
| 583 | Denied. This is not a managed care pilot claim. Rebill using your non-managed care pr… | Details → |
| 589 | Codes not payable in combination. Rebill exam with codes in range of 90671-90695 or Z… | Details → |
| 598 | Action is being taken. Do not send rebill, adjustment or appeal until you receive not… | Details → |
| 599 | Action is being taken. Do not send rebill, adjustment or appeal until you receive not… | Details → |
| 600 | Return letter for inpatient hospital bills containing multiple charges for unrelated … | Details → |
| 601 | Return letter for inpatient hospital bills containing multiple charges during a perio… | Details → |
| 602 | Return letter for inpatient bills where CPT procedure codes have been used instead of… | Details → |
| 603 | Return letter for returning non-payable bills to unlicensed providers. | Details → |
| 604 | Return letter for ungrouped CPT codes on hospital bills. | Details → |
| 605 | Letter to return adjustment requests for hospital bills previously adjusted as a resu… | Details → |
| 606 | Return letter (for providers) explaining that L&I is not "copay". | Details → |
| 607 | Return letter for inpatient DRG interim bill. | Details → |
| 608 | Return letter (for workers) explaining that L&I is not "co-pay". | Details → |
| 609 | Return letter for invalid inpatient hospital ICD codes. | Details → |
| 610 | Return letter for problem with principal (first) diagnosis on hospital bill. | Details → |
| 611 | Return letter for hospital bill with invalid data. | Details → |
| 612 | Return letter for inpatient hospital bill with invalid age or sexcode data. | Details → |
| 613 | Return letter for skilled nursing facility charge submitted on a UB92. | Details → |
| 614 | Return letter for inpatient hospital bills that have invalid data and DRG cannot be a… | Details → |
| 617 | Return letter for possible duplicate bill. | Details → |
| 621 | Return letter for late charges that must be requested by adjustment to previously pai… | Details → |
| 622 | Return letter for inpatient bill with invalid units of service for room charges. | Details → |
| 623 | Return letter for IP bill submitted without prior notification and selected for audit… | Details → |
| 624 | Return letter for IP bill regarding admit & discharge dates being equal. | Details → |
| 625 | Letter to return adjustment requests for hospital bills previously adjusted as a resu… | Details → |
| 626 | Return letter for inpatient bill with invalid units of service for room charges. | Details → |
| 628 | Return Letter for denied services on Managed Care Claims. | Details → |
| 629 | Rtn ltr for bills submitted on wrong bill form. Provider instructed to resubmit charg… | Details → |
| 630 | Return letter for negative charges billed. Provider instructed to resubmit bill listi… | Details → |
| 631 | Return letter for bill that is not related to a Washington State Worker's Compensatio… | Details → |
| 632 | Return letter for compounded prescriptions billed on wrong bill form. | Details → |
| 633 | Return letter for IP bill with incorrect information. | Details → |
| 634 | Return letter for IP bill for services submitted within 24 hours. | Details → |
| 635 | Return letter for bill using "old" and "new" IME codes. Provider instructed to resubm… | Details → |
| 636 | Return letter for IP bill regarding admit & discharge dates being equal. | Details → |
| 637 | Return letter for IP bill for incorrect information on bill. | Details → |
| 640 | Return letter for IME bill. Another bill for this date of service was previously paid… | Details → |
| 641 | Return letter for bill using out-of-date procedure code for a disability rating or an… | Details → |
| 645 | Return letter for compound drugs billed incorrectly. | Details → |
| 650 | Return letter for vocational travel expense billings with incomplete or missing infor… | Details → |
| 651 | Return letter for hospital bills that don't have itemized detail. | Details → |
| 653 | Return letter for bills submitted for which no claim exists in the Department for cla… | Details → |
| 654 | Return letter for Misc & HCFA billing which have multiple missing/invalid detail incl… | Details → |
| 655 | Return letter for IH hospital bills which have multiple missing detail including bill… | Details → |
| 656 | Return letter for pharmacy bills which have multiple missing/invalid detail including… | Details → |
| 657 | Return letter for claimant travel bills which have multiple missing detail including … | Details → |
| 658 | Return letter for bills received on wrong bill form including billing which is for mo… | Details → |
| 659 | Return letter for hospital bills which did not have a summary charge sheet of revenue… | Details → |
| 660 | Return letter for vocational bills on which too many line items have been included in… | Details → |
| 661 | Return letter for bill on claims in abeyance. | Details → |
| 662 | Return letter for possible dup bills when the previously paid bill was paid for a dat… | Details → |
| 663 | Return letter for travel vouchers. | Details → |
| 664 | Return letter for lines that are illegible/unreadable. | Details → |
| 665 | Return letter to claimant who has requested reimbursement for services which he paid. | Details → |
| 666 | Return letter for bills with dates of service greater than 12 months old. | Details → |
| 667 | Return letter to claimant or provider who has requested reimbursement or billed for s… | Details → |
| 668 | Return letter for claims before the appeals board. | Details → |
| 669 | Return letter for claims where reopening action is pending. | Details → |
| 670 | Blank return letter. | Details → |
Medical claim denial codes — formally known as Claim Adjustment Reason Codes (CARC) — are standardized identifiers maintained by the X12 standards body and used across all Medicare, Medicaid, and commercial payer 835 electronic remittance transactions. When a claim is paid at a different amount than billed, at least one CARC code must accompany the remittance advice to indicate the specific reason for the adjustment.
The most frequently encountered codes include CO-16 (missing or invalid claim information), CO-45 (charges exceeding fee schedule), PR-1 (patient deductible), CO-29 (timely filing deadline exceeded), and CO-4 (procedure code inconsistent with modifier). Each represents a distinct, actionable reason that has a defined resolution pathway.