POTENTIAL FOR BIAS IN SEVERITY ADJUSTED HOSPITAL OUTCOMES DATA - ANALYSIS OF PATIENTS WITH RHEUMATIC DISEASE

Objective. To examine the predictive validity of MedisGroups, a widely used method of measuring severity of illness, among patients with rhe umatic disease and identify determinants of hospital outcomes, after a djusting far severity of illness. Methods. Adult medical and surgical patients with rheumatic disease (5421) admitted to an academic medical center in 1988-90 were studied using a retrospective cohort design. S ociodemographic, clinical, and financial data were obtained from compu terized hospital information systems. Severity of illness on admission was determined for each patient using MedisGroups, which classifies p atients into groups of increasing severity. Results. MedisGroups admis sion severity groups were highly related (p < 0.001) to inhospital mor tality rates, which were 0.4, 0.8, 5.1 and 16.1%, respectively among p atients in 4 groups of increasing severity. Controlling for MedisGroup s admission severity using logistic regression, age, admission from th e emergency room, and transfer from an acute care hospital were found to be additional independent predictors of mortality. MedisGroups seve rity groups were also directly related (p < 0.001) to length of stay a nd total hospital charges. Controlling for admission severity using li near regression, length of stay, and charges were independently relate d to several other variables, for example, length of stay was greater for patients admitted from the emergency room or transferred from othe r hospitals and for nonwhites; women, and older patients. Finally, wit hin common individual diagnoses, these factors substantially increased the amount of variance in length of stay and charges explained by Med isGroups alone. Conclusions. Our findings demonstrate that after adjus ting for severity of illness using MedisGroups, several other easily m easured variables were associated with hospital outcomes in patients w ith rheumatic disease. Thus, generic severity systems, such as MedisGr oups, may not adequately adjust outcomes among patients with rheumatic disease. Comparative hospital data based on these systems may be subj ect to bias.