ILLNESS SEVERITY ADJUSTMENT FOR OUTCOMES ANALYSIS - VALIDATION OF THEICISS METHODOLOGY IN ALL 821,455 PATIENTS HOSPITALIZED IN NORTH-CAROLINA IN 1996

Background. Previous work has demonstrated that the International Clas sification of Diseases 9th Revision (ICD-9) Based Illness Severity Sco re (ICISS) methodology developed by Rutledge and Osler can perform wel l in this role as a severity adjustment tool in trauma patients. The p urpose of the present study was to extend this previous work to determ ine the ability of ICISS to predict outcomes in all types of hospitali zed patients. Methods. The ICISS methodology was used to derive predic tions of survival, length of hospital stay, and hospital charges in th e entire study population. Results. A total of 821, 455 hospitalized p atients in North Carolina in 1996 had complete data available for anal ysis. The overall hospital mortality rate was 2.9%. ICISS was an accur ate predictor of hospital survival in all hospitalized patients (accur acy 95.9%, sensitivity 97.2%, and specificity 52.7%.) The area of the receiver operator characteristic curve was 0.93, By adding age to the model, the area under the receiver operator characteristic curve incre ased to 0.95. ICISS also explained a large amount of the variance in h ospital stay and charges (R-2 = 0.38 and 0.56, respectively, P < .0001 ). Conclusions. This study extends previous work suggesting that ICISS may be an important improvement over. Other presently available sever ity adjustment models. If these findings are confirmed in comparison w ith other predictive tools, ICISS may find an important place in asses sing illness severity.