Major revisions to CPT made in 1991 resulted in which of the following?

The correct choice highlights that the major revisions to the Current Procedural Terminology (CPT) in 1991 primarily focused on the evaluation and management (E/M) services. This significant overhaul was designed to better account for the complexity of patient encounters and to ensure that reimbursement was more accurately reflective of the work performed by healthcare providers.

The revisions included the introduction of more detailed guidelines for E/M documentation, leading to clearer standards that dictate how services are classified based on the level of complexity, time spent, and the nature of the presenting problem. This was a crucial development as it aimed to enhance the accuracy and clarity in the coding of E/M services, which are fundamental to billing and reimbursement processes in healthcare.

The other options, while relevant to the overall structure of the CPT, do not directly correlate to the major changes made in 1991. Category II and III codes, for instance, were developed to provide additional tracking and emerging technology coding, which followed later revisions. Modifiers and guidelines, while important for the correct application of codes, were refined in various updates but do not reflect the primary focus of the 1991 revisions as it pertained specifically to E/M services.