CO-10: diagnosis inconsistent with patient gender.

What X12 says CARC 10 means

The diagnosis is inconsistent with the patient's gender.

CARC 10 · Start 01/01/1995, last modified 07/01/2017.

X12 usage note: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present.

In plain terms: The diagnosis does not fit the patient's gender.

What it means on a remittance

The payer compared the diagnosis code with the patient’s gender on file and found a mismatch. CARC 9 is the same edit for age, and CARC 7 covers the procedure code and gender. The X12 usage note points to the 835 Healthcare Policy Identification Segment for the payer’s policy reference.

Typical causes

• The sex field on the claim is wrong or was left at a default.
• A diagnosis code for the wrong anatomy or condition was picked.
• The patient’s gender on the payer’s file differs from your record.
• The claim was billed under another person’s record.

These are common billing patterns, not a diagnosis of your claim. The remittance and the payer's policy decide.

What to check

1. Compare the patient sex on the claim with registration and the insurance card.
2. Re-read the diagnosis code descriptor against the visit note.
3. Check that the claim is under the right patient and subscriber.
4. Read the REF segment of the 835, if present.

Correct, resubmit or appeal

If the sex field or the diagnosis code was wrong, correct it and resubmit. If both are right, send the payer the clinical record that supports the diagnosis and ask for a review through its appeal process.

Medicare dates that apply

A Medicare redetermination request must be filed within 120 calendar days from the date a party receives the notice of the initial determination; receipt is presumed 5 calendar days after the notice date unless there is evidence to the contrary (42 CFR 405.942(a)), and a late request can be considered for good cause (405.942(b)). Other payers set their own appeal windows in the contract or plan documents, so read the notice for the date. The tool above runs the date math.

Related codes

X12 does not publish a table that pairs each code with remark codes; the payer picks the remark code and prints it beside the CARC on the same remittance line.

Other codes: CARC 6 (procedure vs. age), CARC 16 (missing or wrong claim data) and the full lookup.

Worked example (hypothetical)

A claim denies with CO-10. The registration clerk had left the sex field at a default value. The biller corrects it to match the patient’s record and resubmits.

Sources

• X12: Claim Adjustment Reason Codes — code text, usage notes and dates (list dated 10/30/2026, retrieved 2026-11-02)
• 42 CFR 405.942 — eCFR, current through 2026-10-29 (retrieved 2026-11-02)

Code descriptions are X12 copyrighted material, quoted here only for the codes on this page and linked to the owner. For the full lists, use X12. The X12 text and the Medicare rule above were read from these pages on November 2, 2026. Causes, checks and examples are general billing practice written for this page, not X12 content. Payers revise code lists, contracts and policies, so confirm anything that affects a claim or a deadline with the payer.