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CO-11 Denial Code: Diagnosis Inconsistent With Procedure

CO-11 means the payer decided the diagnosis codes on the claim do not support the procedure billed. It is usually a diagnosis-to-procedure pairing edit, often driven by coverage policies such as Medicare LCDs and NCDs, or by a wrong diagnosis pointer.

Quick facts

Code
CO-11 (CARC 11)
Status
Active In use since January 1, 1995; last modified July 1, 2017.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The usual group. The provider is responsible for the denied amount unless the claim is corrected or the denial is overturned.
  • PR (Patient Responsibility): Used when the patient is held liable, for example after signing a valid advance notice such as a Medicare ABN. Only then may you bill the patient.
Official description
The diagnosis is inconsistent with the procedure. Usage: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-11 means

CARC 11 says the diagnosis is inconsistent with the procedure. The payer looked at the ICD-10-CM codes linked to a service line and concluded they don’t justify the procedure. The link is made through the diagnosis pointer in box 24E, which points to one or more of the diagnoses in box 21.

Many payers maintain lists of diagnoses that support particular services. For Medicare, these come from National Coverage Determinations (NCDs) and Local Coverage Determinations (LCDs) with their billing and coding articles. Commercial payers publish their own medical and payment policies. When the linked diagnosis isn’t on the list, CO-11 is the result.

Example: a lab test covered only for certain conditions is billed with a routine screening diagnosis. The test was performed and documented, but the diagnosis pointed to does not appear on the covered list, so the line denies.

Common causes

  • Wrong diagnosis pointer. Line 2 points to diagnosis A when it should point to diagnosis C.
  • Only the primary diagnosis linked, when a secondary diagnosis is what supports the service.
  • Non-specific codes. An unspecified code where the policy requires a specific one.
  • Diagnosis not on the covered list in the LCD, NCD, or payer policy.
  • Screening versus diagnostic confusion, where a screening Z code is linked to a diagnostic service or the reverse.
  • Ordering provider’s diagnosis not passed through to the performing provider, common for labs and imaging.

How to fix it

  1. Read the remark code and policy reference. N115 points to an LCD; the 835 REF segment may name the specific policy.
  2. Pull the policy and compare its covered diagnoses to what was documented.
  3. Check box 21 and 24E. Confirm all documented, relevant diagnoses are listed and each line points to the right ones.
  4. If coding or pointers were wrong, send a corrected claim with resubmission code 7 and the original claim number in box 22.
  5. If the claim was right, request reconsideration or appeal with the medical record and a short explanation of medical necessity.
  6. Bill the patient only when allowed, such as when a valid advance notice was signed and the payer reports PR.

How to prevent it

  • Check coverage policies before scheduling high-risk services like certain labs, imaging, and procedures.
  • Get complete diagnosis information from ordering providers, not just a general reason for the order.
  • Code to the highest specificity the documentation supports.
  • Use advance notices appropriately when a service may not meet coverage criteria.
  • Scrub claims against LCD and payer policy lists. A Claims Validator can flag diagnosis and procedure pairs that commonly fail.

See also preventable medical claim denials for how diagnosis errors fit into broader denial patterns.

Specialty notes

Labs, radiology, and cardiology services are the most frequent targets of diagnosis-to-procedure edits because many of their services have detailed coverage policies. Behavioral health claims hit CO-11 when a medical diagnosis is linked to a psychotherapy service instead of the mental health diagnosis being treated.

Remark codes that may appear with CO-11

  • M76 (Missing/incomplete/invalid diagnosis or condition.): The diagnosis is missing, incomplete, or invalid for this service.
  • N115 (This decision was based on a Local Coverage Determination (LCD).): The decision was based on a Local Coverage Determination, which lists covered diagnoses for the service.
  • M25 (The information furnished does not substantiate the need for this level of service.): The information submitted does not substantiate the need for this level of service.
  • CO-50 (These are non-covered services because this is not deemed a 'medical necessity' by the payer.): Not medically necessary, a broader medical necessity denial that may require records review.
  • CO-167 (This (these) diagnosis(es) is (are) not covered.): The diagnosis itself is not covered by the plan.
  • CO-146 (Diagnosis was invalid for the date(s) of service reported.): The diagnosis was invalid for the date of service, for example a deleted or truncated code.
  • CO-16 (Claim/service lacks information or has submission/billing error(s).): Missing or invalid claim information, sometimes used when the diagnosis is absent altogether.

CO-11 FAQ

What is the most common cause of CO-11?

A diagnosis pointer in box 24E that points to a diagnosis that doesn't support that line, or a diagnosis not on the payer's covered list for the service, such as an LCD's covered ICD-10-CM codes.

Should I correct or appeal a CO-11 denial?

If the documentation supports a different or additional diagnosis that was left off, or the pointer was wrong, send a corrected claim. If the claim was coded correctly and the service was medically necessary, appeal with records and the relevant policy.

Can I add a diagnosis just to get paid?

Only if the medical record documents it. Every diagnosis on the claim must be supported by the provider's documentation for that encounter.

Can I bill the patient for CO-11?

Not under CO. If the patient signed a valid advance notice, the payer may report the amount as PR instead, and then you can bill the patient.