Which coding system is primarily used for documentation of outpatient services?

The correct answer is based on the specific function of the coding systems listed in the question. The Current Procedural Terminology (CPT) is primarily used for documenting outpatient services, as it provides a comprehensive set of codes that describe medical, surgical, and diagnostic services offered by healthcare providers. These codes allow for uniform reporting and billing for outpatient procedures and consultations, which are essential in the outpatient setting.

CPT codes help ensure that healthcare providers document the services they provide accurately, allowing payers to understand what services were performed, facilitating appropriate reimbursement. In contrast, while ICD-10 codes are used for diagnosing conditions, HCPCS codes encompass not only outpatient services but also other items and procedures, including those provided in outpatient environments. DRG (Diagnosis-Related Groups) pertains mostly to inpatient services and payment systems, making it less relevant for outpatient documentation.

This makes CPT the most applicable coding system specifically targeted at outpatient services, as it directly corresponds with the nature of the care provided in those settings.