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CO-B13 Denial Code: Previously Paid

CO-B13 means the payer believes payment for this claim or service may already have been made in a previous payment. Find the earlier payment before doing anything else; if the services were truly separate, correct the claim to show it.

Quick facts

Code
CO-B13 (CARC B13)
Status
Active In use since January 1, 1995.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The usual group. The line isn't paid again and can't be billed to the patient.
  • OA (Other Adjustment): Some payers use OA, treating the line as already accounted for by an earlier payment.
Official description
Previously paid. Payment for this claim/service may have been provided in a previous payment.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-B13 means

CARC B13 says previously paid. Payment for this claim or service may have been provided in a previous payment. The payer found an earlier payment it believes covers this service, so it won’t pay again.

The wording “may have been” matters. CO-B13 isn’t always an exact match. The payer may have matched a similar service in a time window, a line paid on a different claim, or a service paid to another provider. That’s what separates it from OA-18, which is for exact duplicates.

Common causes

  • Claim resubmitted after payment, when the first ERA wasn’t posted or was misapplied.
  • Corrected claim sent as a new claim, so the payer sees the service twice.
  • Repeat services on the same day without a repeat-procedure modifier.
  • Similar service paid within a frequency window, such as equipment or supplies.
  • Payment made to another provider or TIN in the same organization.
  • Payment posted to the wrong patient or date in your system, leaving an apparent open balance.

How to fix it

  1. Search for the earlier payment by patient, date of service, and procedure, including other TINs in your group.
  2. If you find it, post it correctly and close the line.
  3. If the services were distinct, send a corrected claim with resubmission code 7 in box 22, adding modifiers such as 76, 77, or 91 as applicable and attaching documentation if required.
  4. If another provider was paid, confirm who performed the service and ask the payer to review.
  5. Don’t bill the patient for the line.

How to prevent it

  • Post every ERA promptly and reconcile open balances before resubmitting.
  • Use resubmission codes for corrected claims instead of sending new ones.
  • Apply repeat-service modifiers when the same service really occurs more than once.
  • Track prior payments across TINs. An ERA Analyzer can surface CO-B13 lines alongside the earlier payments they refer to. See also duplicate claim denials.

Remark codes that may appear with CO-B13

  • M86 (Service denied because payment already made for same/similar procedure within set time frame.): Payment was already made for the same or a similar procedure within a set time frame.
  • N111 (No appeal right except duplicate claim/service issue.): The service was included in a claim previously billed and adjudicated.
  • N702 (Decision based on review of previously adjudicated claims or for claims in process for the same/similar type of services.): The decision was based on a review of previously adjudicated claims.
  • OA-18 (Exact duplicate claim/service (Use only with Group Code OA except where state workers' compensation regulations requires CO)): An exact duplicate claim, matched on every key field.
  • CO-97 (The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.): Bundled into another service already paid.
  • CO-B10 (Allowed amount has been reduced because a component of the basic procedure/test was paid.): A component of the basic procedure was already paid.
  • CO-151 (Payment adjusted because the payer deems the information submitted does not support this many/frequency of services.): Frequency limits exceeded, sometimes confused with prior payment.

CO-B13 FAQ

How is CO-B13 different from OA-18?

OA-18 is for exact duplicates. CO-B13 is broader: the payer thinks the service may have been paid before, even if the claim isn't identical, for example a similar service in a set time frame or a line paid on another claim.

What should I check first?

Look for an earlier ERA or payment that covers the same patient, date of service, and service. If you find it, post it and close the line.

What if the service was performed twice?

Send a corrected claim with documentation and the appropriate modifier, such as 76 or 77 for repeat procedures, or 91 for repeat lab tests where applicable.

What if the earlier payment went to another provider?

Confirm who performed the service. If another provider was paid in error, ask the payer to review and reprocess with your documentation.

Can I bill the patient for a CO-B13 line?

No. Under CO the payer considers the service already paid or accounted for, so there is nothing new to collect from the patient on that line.