N23 is an alert, not a denial. It tells you the patient's share on this claim may change because another insurance is involved or a benefit maximum applies. Before billing the patient, check for secondary coverage and send the claim there first.
The official wording
The X12 Remittance Advice Remark Code list defines N23 as: "Alert: Patient liability may be affected due to coordination of benefits with other carriers and/or maximum benefit provisions."
What to do
- Check whether the patient has secondary coverage.
- If yes, send the secondary claim with this remittance before billing the patient.
- If a benefit maximum applies, confirm it with the plan, then bill the patient for what the secondary does not cover.
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Questions people ask about N23
Is N23 a denial?
No. It is an alert remark code.
Should I bill the patient when I see N23?
Not until you have checked other coverage. The patient's share may be lower once the secondary pays.
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Timely filing limits by payer: Cigna timely filing limit · HealthSpring timely filing limit · Aetna timely filing limit · UnitedHealthcare timely filing limit · Humana timely filing limit · corrected claim timely filing limits
Sources: X12 Remittance Advice Remark Code list (N23), read October 12, 2026; CMS Medicare guidance where Medicare rules are mentioned. Last reviewed October 12, 2026. General information, not coding or legal advice. Payer rules differ, so check the remark code and the payer's own policy.