Providers may continue to use modifier 59 in 2015 in any instance in which it was correctly used prior to January 1, 2015. The Centers for Medicare & Medicaid Services (CMS) recently established four new modifiers (XE, XP, XS, XU) as subsets of modifier 59 to further define Distinct Procedural Service.
CMS plans to introduce these modifiers in a gradual and controlled manner, providing additional guidance and education for appropriate usage. The additional information provided by CMS will contain descriptive information about the new modifiers and will describe specific situations for when each should be used. If providers choose to use the new modifiers, they must be used properly with their published definition.
More information can be found here.