N351N-series (general use)Coverage & Eligibility
N351: Service date outside approved treatment plan
The service happened outside the date span of the approved treatment plan or authorization — common in therapy, home health, and behavioral health.
Commonly appears with these denial codes
The denial code gives the category; N351 pinpoints the specific problem. Read them together before touching the claim.
What to do about it
Compare DOS against the auth/treatment plan window. Request a retro-extension if care legitimately continued, or obtain a new plan period going forward.
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