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CO-6 Denial Code: Procedure Inconsistent With Patient Age

CO-6 means the payer's edits found the procedure or revenue code inconsistent with the patient's age, based on the date of birth on the claim. Either the DOB is wrong, an age-specific code was chosen incorrectly, or the service falls outside the payer's age limits.

Quick facts

Code
CO-6 (CARC 6)
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 absorbs the denied amount unless the claim is corrected or the denial is overturned on appeal.
  • PR (Patient Responsibility): Sometimes used when the service is outside plan age limits and the patient accepted financial responsibility in advance. Verify before billing.
Official description
The procedure/revenue code is inconsistent with the patient's age. 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-6 means

CARC 6 says the procedure or revenue code is inconsistent with the patient’s age. Payers run age edits that compare the patient’s age on the date of service, calculated from the date of birth in box 3, with the age range each procedure or revenue code allows. If they do not match, the line is denied.

Many code sets are age-specific. Preventive medicine visits, some vaccine and administration codes, developmental screenings, and certain neonatal or pediatric services are defined by age band. A code intended for a 1 to 4 year old billed for a 7 year old will fail this edit even though the service was real and documented.

The usage note points to the 835 Healthcare Policy Identification segment, where the payer may identify the age policy it applied.

Common causes

  • Wrong date of birth on the claim, in the practice management system, or in the payer’s enrollment file.
  • Age-banded code chosen for the wrong age, especially preventive visits and screening services near a birthday.
  • Birthday between scheduling and service. The code picked at scheduling no longer fits on the date of service.
  • Newborn billed under the parent’s information, so the claim carries the parent’s DOB.
  • Plan age limits, for example a service the plan covers only for children or only for adults.
  • Revenue code limits on institutional claims, such as nursery or pediatric revenue codes billed for an adult.

How to fix it

  1. Check the DOB on the claim against the patient’s ID card and the payer’s eligibility response.
  2. Recalculate the patient’s age on the date of service and confirm the code’s age range.
  3. If the DOB was wrong, correct it in your system and ask the payer to correct its record if theirs is wrong, then send a corrected claim (resubmission code 7 in box 22).
  4. If the code was wrong, select the correct age-appropriate code, update the documentation if needed, and send a corrected claim.
  5. If both were right, appeal with documentation showing medical necessity for this patient, or confirm with the payer whether the service is excluded by age.
  6. Do not bill the patient for a CO-6 denial.

How to prevent it

  • Verify DOB at registration by comparing the ID card, photo ID, and eligibility response.
  • Build age checks into charge entry for age-banded code families.
  • Recheck codes on the date of service for patients whose birthday falls between scheduling and the visit.
  • Validate before submission. A Claims Validator check can flag an age-banded code that does not match the patient’s DOB.

Specialty notes

Pediatric and family practices hit CO-6 most often, around preventive visit and immunization codes at age thresholds. Newborn claims billed before the baby has their own member ID are another frequent source; see CO-34 for newborn coverage issues.

Remark codes that may appear with CO-6

  • N329 (Missing/incomplete/invalid patient birth date.): The patient's date of birth is missing, incomplete, or invalid, which points to a data error rather than code choice.
  • N129 (Not eligible due to the patient's age.): Not eligible due to the patient's age: the plan's age limit for this service is the issue.
  • N56 (Procedure code billed is not correct/valid for the services billed or the date of service billed.): The procedure code is not valid for the service billed, often an age-banded code chosen for the wrong age.
  • CO-9 (The diagnosis is inconsistent with the patient's age.): The diagnosis, rather than the procedure, conflicts with the patient's age.
  • CO-7 (The procedure/revenue code is inconsistent with the patient's gender.): The procedure conflicts with the patient's gender instead of age.
  • CO-14 (The date of birth follows the date of service.): Date of birth is after the date of service, a pure data error.
  • CO-31 (Patient cannot be identified as our insured.): Patient cannot be identified, which can also come from a mismatched date of birth.

CO-6 FAQ

What causes a CO-6 denial?

Most often a wrong date of birth on the claim or in the payer's records, or an age-banded code (such as preventive visit or vaccine administration codes) selected for the wrong age group. Sometimes the service is simply outside the age range the payer covers.

How do I fix CO-6?

Compare the DOB on the claim to the insurance card and payer eligibility response. If the DOB or code was wrong, send a corrected claim with resubmission code 7. If both were correct, appeal with documentation.

Can I bill the patient for CO-6?

Not under the CO group code. The provider is responsible unless the payer changes the group code or the patient signed a valid financial responsibility agreement that the payer recognizes.