CO-9 Denial Code: Diagnosis Inconsistent With the Patient’s Age

CO-9 is Claim Adjustment Reason Code 9 with group code CO. CARC 9 means the dx is does not match the patient age. Age edits are payer checks that compare ICD-10-CM codes to date of birth. If a pediatric, newborn, adult-only, or geriatric code does not fit the patient’s age, the payer rejects or adjusts the line. Before this page existed, a WordPress 404 guess sent /denial-codes/co-9/ to CO-96. CO-96 means non-covered charges. That is a different problem. Many people search for “co 9 denial code”, and that is the phrase this page answers. (Primary sources: X12 Claim Adjustment Reason Codes · CMS Claims Processing Manual, Ch. 22, §60.1 · our CO-11 and CO-96 guides)

Quick answer: Match the billed diagnosis to the patient’s date of birth. If the ICD-10-CM code is age-restricted (newborn, pediatric, adult-only, or geriatric), correct the diagnosis from the record or fix a wrong DOB/patient data field, then resubmit. Do not treat CO-9 as a non-covered benefit denial like CO-96.

Part of our denial codes library. Written by Manikandan, a revenue cycle management specialist with more than 10 years of US medical billing experience. Last reviewed: 14 October 2026. Official code wording is quoted word for word from X12; Medicare rules link to their CMS source.

CO-9 denial code description (official X12 wording)

X12 Claim Adjustment Reason Code 9, verbatim:

“The diagnosis is inconsistent with the patient\’s age. Usage: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present.”

Source: X12 Claim Adjustment Reason Codes, checked 14 October 2026. Start: 01/01/1995. Last Modified: 07/01/2017.

The CARC is 9. The group code is usually CO (contractual / not payable as billed). Always read any health-policy ID REF on the 835 when present.

What CO-9 means in plain English

• The payer compared the dx code(s) to the patient’s age (from DOB and date of service).
• An age edit is a system rule that blocks codes outside an allowed age band.
• CO-9 is a coding and patient data denial. It is not a statement that the plan excludes the benefit.
• CO-6 means the service or revenue code failed an age edit. That is different from a dx age edit.
• CO-96 means non-covered charges. That is a benefit issue, not an age-vs-dx match.
• CO-11 means the dx is does not match the service, not with age.

CO-9 vs CO-6, CO-11, CO-96 and lookalikes

Code	Official X12 idea	What it tells you
CO-9	Dx does not match patient’s age	ICD vs DOB mismatch — this page
6	Service/revenue code does not match patient’s age	CPT/HCPCS or revenue code failed an age edit (not dx)
CO-11	Dx does not match the service	Dx does not support the service — CO-11
10	Dx does not match patient’s gender	Dx vs sex edit — CO-10 (this batch)
240	Dx does not match patient’s birth weight	Neonatal weight edit
96	Non-covered charge(s)	Benefit / coverage — CO-96
109	Not covered by this payer; send to correct payer	Wrong payer — CO-109

Before this page existed, WordPress’s 404 guess sent /denial-codes/co-9/ to CO-96. Non-covered and age-mismatched dx are not the same denial.

Common triggers for CO-9

CO-9 means the dx and the patient age do not match. Common causes:

1. Wrong ICD-10-CM chapter or age-restricted code. For example, newborn (P) codes, pediatric-only codes, or adult-onset codes billed on the wrong age band.
2. Stale or swapped patient data. DOB transposed, year off by a digit, or the wrong patient selected in the PMS.
3. Copy-forward dx. Prior encounter dx codes reused without checking current age (especially across birthdays or from maternal to newborn charts).
4. Screening / wellness codes with age limits in payer policy or NCD/LCD age criteria.
5. Secondary dx left on the claim that the primary payer’s editor flags even when the principal dx is fine.

Where CO-9 shows up in the 835

CLP*PCN99221*1*185.00*0*185.00*12*CLAIM778899~
SVC*HC:99213*185.00*0**1~
CAS*CO*9*185.00~
REF*HPI*AGE-DX-EDIT~

• Line paid $0.
• CAS*CO*9 took the full charged/allowed amount as an age-vs-dx inconsistency adjustment.
• Optional REF*HPI (health-policy ID) may name the payer’s age-dx edit.
• Sample only. Real remits vary; save the full CAS and any remark codes.

How to fix CO-9: decision path

1. Confirm CAS*CO*9 (or PR/OA*9 if grouped differently) and capture any RARC or policy REF.
2. Pull the claim patient data. Date of birth, sex, and date of service must match the chart and benefit check.
3. List every ICD-10-CM code on the claim. Check each against ICD-10-CM age notes, your encoder’s age edits, and the payer’s policy.
4. If the dx is wrong, correct it from the records (query the clinician if needed) and submit a corrected claim.
5. If the DOB is wrong, fix the patient record and benefit check mirror, then resubmit.
6. If both dx and age are correct but the payer’s edit is outdated or too strict, appeal with medical records, coding rules, and the clinical rationale for that age.
7. Do not rebill as CO-96/non-covered or write it off as a benefit exclusion without checking the dx-vs-age pair.
8. Train coders that age edits apply to dx (CARC 9) separately from service/revenue age edits (CARC 6).

Medicare, commercial and Medicaid notes

Medicare. Age-related dx edits appear in claim scrubbing and medical-review logic. When a health-policy ID segment is present on the 835, use it to find the specific edit. Corrected claims must still meet timely filing.

Commercial. Many plans load ICD age edits from clearinghouse or encoder libraries. Portal remittance notes often say “dx not valid for age” — that maps to CARC 9, not to a generic non-covered code.

Medicaid. State systems may apply stricter pediatric or maternity age bands. Confirm the state’s companion guide and any age-linked dx lists before appealing.

Worked example

Here is an example from a typical pediatric claim:

A 14-year-old is seen for a routine office visit. The claim carries a newborn-period dx left over from an imported problem list. The remit returns CAS*CO*9 for the line.

Prevention checklist

• [ ] Run encoder / claim-scrubber age-vs-dx edits before filing.
• [ ] Re-verify DOB on every new patient and after chart merges.
• [ ] Purge newborn and maternity codes from problem lists when age no longer fits.
• [ ] Separate CARC 9 (dx vs age) from CARC 6 (service vs age) in denial workqueues.
• [ ] Do not confuse CO-9 with CO-96 (non-covered) or CO-11 (dx vs service).
• [ ] Keep the CARC and RARC guide handy for staff training.

Related denial codes

• CO-11: dx does not match the service.
• CO-10: dx does not match the patient sex.
• CO-96: non-covered charge(s) — the old wrong redirect target.
• CO-16: claim/service lacks information or has filing/billing error(s).
• CARC and RARC guide.

Key takeaways

CARC 9 means the dx does not fit the patient’s age. Fix the ICD code, the DOB, or both; then resubmit or appeal with records. CO-9 is not CO-96. Non-covered benefits and age-vs-dx edits are different workflows.

FAQ

Quick facts

Item	Value
X12 code	9
X12 start	01/01/1995
Last modified	07/01/2017
Official wording	The dx is does not match the patient age
Usual group	CO
Common confusions	CO-6 (service vs age), CO-96 (non-covered)
Last reviewed	14 October 2026

Sources

• X12, Claim Adjustment Reason Codes (CARC 6, 9, 10, 11, 96, 109, 240). CARC 9 Start 01/01/1995; Last Modified 07/01/2017. Accessed 14 Oct 2026.
• CMS, Medicare Claims Processing Manual (IOM 100-04), Ch. 22, §60.1 Group Codes. Accessed 14 Oct 2026.
• Medical Billing 101, CO-11 guide.
• CMS, ICD-10 page (coding & billing). Accessed 14 Oct 2026.
• Medical Billing 101, CO-96 guide.

Code wording and Medicare rules on this page were checked on 14 October 2026 against X12 and CMS sources.

Last reviewed: 14 October 2026 · This page is educational and doesn’t replace payer-specific contracts or coding rules.