The Medicare National Correct Coding Initiative (NCCI) and related editing defines codes that should not be reported together either in all situations or in most situations. Modifier 59 is used to identify procedures/services, other than E/M services, that are not normally reported together, but are appropriate under the circumstances. Documentation must support the use.
Note: Modifier 59 and other associated modifiers should not be used to bypass editing unless the proper criteria for use of the modifier are met.
For more details on the appropriate and inappropriate uses of modifier 59, including numerous coding examples, here is the link to the MLN Matters® article SE1418.