How it works
NCCI has two main kinds of edit. Procedure-to-procedure (PTP) edits list pairs of codes where one is normally included in the other; each pair has an indicator showing whether a modifier can ever allow both to be paid. Medically unlikely edits (MUEs) set the maximum units of a code normally reported for one patient on one date. CMS updates the edits quarterly; Medicaid programs use them too, and many commercial plans apply them or similar edits.
Why it matters
Claims that break NCCI edits are denied or partly paid, and using a modifier to bypass an edit without documented justification creates compliance risk. Checking edits before submission prevents both.
Example
Two procedures performed at different anatomic sites form an NCCI pair that allows a modifier. Because the note documents separate sites, the coder adds modifier XS (or 59) and both are paid. See medical coding.