The Impact of Principal Diagnosis on Readmission Risk among Patients Hospitalized for Community-Acquired Pneumonia

Coding variation distorts performance/outcome statistics not eliminated by risk adjustment. Among 1596 community-acquired pneumonia patients hospitalized from 1998 to 2012 identified using an evidence-based algorithm, the authors measured the association of principal diagnosis (PD) with 30-day readmission, stratified by Pneumonia Severity Index risk class. The 152 readmitted patients were more ill (Pneumonia Severity Index class V 38.8% versus 25.8%) and less likely to have a pneumonia PD (52.6% versus 69.9%). Among patients with PDs of pneumonia, respiratory failure, sepsis, and aspiration, mortality/readmission rates were 3.9/8.5%, 28.8/14.0%, 24.7/19.6%, and 9.0/15.0%, respectively. The nonpneumonia PDs were associated with a greater risk of adjusted 30-day readmission: respiratory failure odds ratio (OR) 1.89 (95% confidence interval [CI], 1.13-3.15), sepsis OR 2.54 (95% CI, 1.52-4.26), and possibly aspiration OR 1.73 (95% CI, 0.88-3.41). With increasing use of alternative PDs among pneumonia patients, quality reporting must account for variations in condition coding practices. Rigorous risk adjustment does not eliminate the need for accurate, consistent case definition in producing valid quality measures.