Composite parameters including serum HO-1, age, sex, and partial pressure of oxygen in arterial blood/fraction of inspired oxygen (P/F) ratio for prediction of 3-month mortality showed a higher AUC (ARDS: 0.925, AE-ILDs: 0.892) than did AUCs of a single predictor or combination of two or three predictors. The gene discussed is HMOX1; the disease is acute respiratory distress syndrome.