The Computerized Severity Index. A new tool for case-mix management.

We describe the new Computerized Severity Index (CSI) that is obtained from an expanded discharge abstract data set, based on a 6th-digit severity addition to the ICD-9-CM coding system. The new 6-digit code book (called ICD-9-CMSA) is used to label existence and severity of each principal and secondary diagnosis. It can be used to produce an overall severity of illness level for each hospital inpatient. The impact of severity-adjusted DRGs on prospective payment and uses of the CSI for assessing quality of care, efficiency, physician practice profiles, and prediction of posthospital resource needs are discussed.