Which modifier correctly indicates that the procedure was performed on the left index finger?

The modifier indicating that the procedure was performed on the left index finger is indeed -F1. This modifier is specifically designated in the Current Procedural Terminology (CPT) coding system to describe procedures involving the left index finger.

Using this modifier communicates to billing and coding offices that the procedure is related to the left hand's specific finger, ensuring accurate documentation and reimbursement for the service provided. Each digit modifier represents a different finger or specific sites on the hands, and understanding these distinctions helps maintain clarity in medical billing practices.

The other modifiers, -F2, -F3, and -F4, correspond to other fingers or sites, such as the middle finger, ring finger, and little finger, respectively. Therefore, using the appropriate modifier is crucial for compliance and accuracy in coding.