CO-11 at a glance
CO-11 | |
|---|---|
Group code | CO, Contractual Obligation (X12) |
CARC 11 text (X12) | The diagnosis is inconsistent with the procedure. |
X12 usage note | Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present |
In the X12 list since | January 1, 1995. Last modified July 1, 2017 |
What it means for a therapy practice | The diagnosis the line points to isn't one the payer accepts for that CPT code |
Who owes the denied amount | Nobody yet. Under CO, it can't be moved to the client |
Usual fix | Correct the pointer or the diagnosis to match the note, then send a corrected claim |
What CO 11 means on a remittance
CARC 11 is one of a small family of consistency codes. Each compares the diagnosis or the procedure with one other fact on the claim and reports a mismatch. Code 11 compares the diagnosis with the procedure. Its siblings compare the diagnosis with the patient's age (9), gender (10) or the provider type (12).
The check runs per service line, not per claim. A claim can carry a perfectly good mental health diagnosis and still get CO‑11 on one line, if that line points somewhere else.
Start with the diagnosis pointer
On a CMS‑1500, box 21 holds up to 12 diagnoses, lettered A to L. Box 24E on each service line holds the pointer: the letter of the primary diagnosis for that line. Medicare asks for a single letter per line, and some commercial payers accept more than one. The electronic 837P works the same way. The payer's edit reads the pointer, not the whole list.
Here is how that goes wrong for a fictional couple seen for conjoint sessions. The identified client has adjustment disorder with mixed anxiety and depressed mood. The claim lists:
Box 21 | Code | Official description (FY2027) |
|---|---|---|
A | Z63.0 | Problems in relationship with spouse or partner |
B | F43.23 | Adjustment disorder with mixed anxiety and depressed mood |
The 90847 line points only to A. This client's plan doesn't accept a Z code as the sole diagnosis for family psychotherapy, and the line comes back CO‑11. Nothing is wrong with the diagnoses. The pointer should read B, or B then A. A corrected claim with the pointer changed is the whole fix, as long as the progress note documents the F43.23 diagnosis and how the conjoint session treats it.
Whether a Z code alone is accepted varies by plan. Some pay couples work with Z63.0 on the line, others want the identified client's mental health diagnosis first. Check before the first session, not after the third denial.
Other common causes of CO-11 on therapy claims
- A medical diagnosis carried over from a referral. The referral lists a physical condition, and it lands in box 21 as A. The psychotherapy line points to it by default.
- A screening code with an unrelated diagnosis. A 96127 line pointing to a diagnosis the plan doesn't link to emotional or behavioral screening.
- A payer coverage list. Medicare contractors and many commercial plans publish lists of diagnoses that support a given service. A diagnosis outside the list for that code gets denied, even if it's clinically correct.
- A stale diagnosis. The working diagnosis from intake was never updated, and it no longer matches the service now being billed.
CO-11 vs CO-167, CO-146 and CO-12
CARC | X12 text | The question it answers |
|---|---|---|
11 | The diagnosis is inconsistent with the procedure. | Does this diagnosis fit this service? |
167 | This (these) diagnosis(es) is (are) not covered. | Does the plan cover this diagnosis at all? |
146 | Diagnosis was invalid for the date(s) of service reported. | Was this a valid code on that date? |
12 | The diagnosis is inconsistent with the provider type. | Can this type of provider bill for this diagnosis? |
The difference changes the fix. A CO‑11 is usually a coding correction. A CO‑167 is a coverage question, which may mean the client pays under a signed financial agreement or the plan's appeal process. A CO‑146 can follow the October 1 code‑set change: FY2027 took effect on October 1, 2026, and a diagnosis has to be valid for the date of service, not the date you send the claim.
A header code is a separate problem. F43.2 is a header code for adjustment disorders, not billable on its own in FY2027. A claim needs one of the full codes, such as F43.22 or F43.23. Fix that before you look for a CO‑11 cause.
How to fix CO-11
- Open the denied line and note which diagnosis letters it points to.
- Compare those diagnoses with the progress note for that date. The claim should say what the note says.
- If the pointer is wrong, change it and send a corrected claim, using the payer's resubmission code and the original claim number.
- If the diagnosis is right but the plan doesn't accept it for that service, check the payer's policy and your documentation, then decide between an appeal and a coverage conversation with the client.
- Fix the default in your billing system so the next claim doesn't repeat the same pointer.
Diagnosis pages linked from here: F43.23, F43.22 and F41.1. The procedure pages: 90847, 90837 and 96127.
CPT is a registered trademark of the American Medical Association. CPT codes copyright 2026 American Medical Association. All rights reserved.
If you write progress notes with Twofold, read the diagnosis line in each note before you sign it, since that line is what the claim has to match. Related denial codes: CO-6 for a procedure that doesn't fit the client's age, CO-231 for mutually exclusive services and CO-252 when the payer wants records.
Checked against the X12 Claim Adjustment Reason Code list and the FY2027 ICD‑10‑CM code set on October 26, 2026. CARC 11 was last modified on July 1, 2017, and nothing about it changed this year.