Developed by 3M, APR DRGs stands for All Patient Refined Diagnosis Related Groups, a classification system designed to accurately identify how sick a patient population is compared to peer organizations. 3M APR DRGs are an extension of the basic DRG structure that reflects the complete cross-section of patients seen in an acute care setting. The 3M APR DRGs include four severity-of-illness levels and four risk-of mortality levels within each DRG. Severity and mortality subclasses are assigned according to a sophisticated clinical logic that simultaneously evaluates the interactions of multiple co-morbidities, age, procedures, and principal diagnosis. The idea behind APR DRGs is that severity of illness and risk of mortality both depend on the patient’s underlying condition. High severity of illness and risk of mortality are characterized by multiple serious diseases and the interactions between disorders.