What is the primary function of modifier -S?

The primary function of modifier -S is to signify that a service is secondary to another procedure. This modifier is used to clarify that the procedure being described is not the primary focus of care and is being performed in conjunction with another, more significant procedure. By indicating that one service is secondary, it helps to ensure proper billing and claim processing in cases where multiple procedures are documented for the same patient encounter.

The understanding of secondary services is critical in coding because it affects reimbursement rates, documentation requirements, and the overall clarity of the medical record. Proper use of modifier -S allows healthcare providers to accurately convey the context and relationship between various services rendered.

In contrast, modifiers relating to primary procedures or unrelated conditions would serve different functions and wouldn't convey the same relationship between procedures as modifier -S. Likewise, modifiers that focus on preventive care services do not pertain to the indication that a service is secondary, highlighting the unique application of modifier -S in medical coding.