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CO-B20 Denial Code: Service Furnished by Another Provider

CO-B20 means the payer determined that the procedure or service was partially or fully furnished by another provider, so it won't pay your claim in full, or at all. Two providers are typically billing for the same work, or the wrong provider is on the claim.

Quick facts

Code
CO-B20 (CARC B20)
Status
Active In use since January 1, 1995; last modified September 30, 2007.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The usual group. The provider absorbs the reduction or denial and can't bill the patient.
Official description
Procedure/service was partially or fully furnished by another provider.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-B20 means

CARC B20 says the procedure or service was partially or fully furnished by another provider. The payer has evidence that someone else performed the service, or part of it, and has already billed for that work or is entitled to. It reduces or denies your claim so it doesn’t pay twice for the same service.

This is common where services are naturally shared: surgery with pre- and post-operative care, diagnostic tests with separate interpretation, and care transitions between practices. It also happens when the wrong provider appears on the claim.

Common causes

  • Global surgical packages. The surgeon bills a global package that includes post-operative care, and another provider bills follow-up visits during the global period.
  • Split surgical care not reported with modifiers 54 (surgical care only), 55 (post-operative management only), or 56 (pre-operative management only).
  • Interpretation billed twice, for example by an emergency physician and a radiologist.
  • Care handed off between practices where both billed the same date or service.
  • Wrong rendering provider in box 24J, pointing to someone other than the person who performed it.

How to fix it

  1. Identify the other provider and what they billed. The payer can often tell you.
  2. Confirm what you actually did from your documentation.
  3. Bill your portion only. For shared surgical care, use modifiers 54, 55, or 56 as appropriate, with any transfer-of-care documentation the payer requires. Send a corrected claim with resubmission code 7 in box 22.
  4. Coordinate with the other provider if their claim covers work you performed.
  5. Appeal with documentation if you performed the service and the other claim was wrong.
  6. Don’t bill the patient for CO-B20 amounts.

How to prevent it

  • Check for global surgical periods before billing visits after another provider’s surgery.
  • Document transfers of care in writing between the surgeon and the provider managing follow-up.
  • Agree on interpretation billing with hospitals and radiology groups.
  • Verify the rendering provider on every claim. See provider enrollment denials.

Specialty notes

Ophthalmology, orthopedics, and primary care practices often share surgical care and should use split-care modifiers consistently. Emergency physicians and radiologists should agree on who bills the formal interpretation of imaging.

Remark codes that may appear with CO-B20

  • N290 (Missing/incomplete/invalid rendering provider primary identifier.): The rendering provider identifier is missing, incomplete, or invalid.
  • 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 claims already adjudicated or in process for similar services.
  • M144 (Pre-/post-operative care payment is included in the allowance for the surgery/procedure.): Pre- and post-operative care is included in the surgery allowance, often paid to the surgeon.
  • 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, a similar split-service situation.
  • CO-B13 (Previously paid.): Previously paid, possibly to another provider.
  • CO-54 (Multiple physicians/assistants are not covered in this case.): Multiple physicians or assistants aren't covered for this case.
  • 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, sometimes billed by a different provider.

CO-B20 FAQ

When does CO-B20 usually happen?

When another provider already billed all or part of the same service, such as a surgeon billing a global surgical package that includes post-operative visits you also billed, or two practices billing the same interpretation.

How do I fix CO-B20?

Find out which provider billed and what they billed. If you shared the work, bill only your portion with the right modifier, such as 54, 55, or 56 for split surgical care, and coordinate with the other provider.

What if the other provider billed in error?

Contact the other provider to correct their claim, then ask the payer to reprocess yours with documentation showing you performed the service.

Can I bill the patient for CO-B20?

No. Under CO, the provider absorbs the amount.