Modifier 79 indicates a surgical procedure performed during the postoperative global period of a prior surgery that is unrelated to the original procedure. Per AMA/CPT and CMS guidance, it is appended when the same physician (or same-specialty physician in the same group) performs a distinctly unrelated procedure during the active global period (commonly 0-, 10-, or 90-day). Use requires clear documentation showing the new procedure is for a different diagnosis or anatomical system; when correctly applied it prevents the new procedure from being bundled into the original global package and begins a new global period for the unrelated procedure.

Unlike modifier 78 (which denotes a related procedure or treatment for a complication and does not start a new global period) and modifier 24 (which applies to unrelated E/M services during the postoperative period), modifier 79 is specific to unrelated surgical procedures. When used properly, payers—including Medicare systems recognizing Level I CPT modifiers—should separately reimburse the unrelated procedure rather than reduce payment as part of the initial surgery’s global allowance. Documentation should explicitly support the lack of relation between procedures because disputed or ambiguous cases can lead to denials or audits.

Practical examples illustrate typical use: a urologist performing a cystoscopy for a new urinary diagnosis during the 90-day global period of a prior hydrocelectomy would append modifier 79 to the cystoscopy to indicate it is unrelated and to trigger separate reimbursement; similarly, a surgeon repairing a contralateral fracture occurring after a knee arthroplasty global period began would append modifier 79 to the fracture repair. Always confirm payer-specific rules and consult the current CPT® Professional Edition and relevant Medicare guidance for updates or nuanced policy differences.