The National Correct Coding Initiative (NCCI) initiative's purpose is to define bundled vs. separate codes. NCCI code pair edits are automated prepayment edits that prevent improper payment when certain codes are submitted together for Part B-covered services. NCCI edits are revised, published quarterly and are broken into two tables of edit pairs:
Correct Coding Edits for Column1/Column 2 CPT® codes: Although the Column 2 code is often a component of a more comprehensive Column 1 code, this relationship is not true for many edits. In the latter type of edit the code pair edit simply represents two codes that should not be reported together, unless an appropriate modifier is used.
Mutually Exclusive CPT® code combinations: Many procedure codes should not be reported together because they are mutually exclusive of each other. Mutually exclusive procedures cannot reasonably be performed at the same anatomic site or same beneficiary encounter.
CMS has additional information about how to use NCCI edits. [pdf]
AUA provides current quarterly edits from NCCA for free. NCCI edits can be downloaded from CMS.gov as well.