Spirometric criteria for hospital admission of patients with acute exacerbation of COPD. Recent studies have demonstrated that there is a high relapse rate for patients discharged from the Emergency Department (ED) following treatment of acute exacerbation of chronic obstructive pulmonary disease (COPD). Objective criteria have not been established to determine when to hospitalize these patients. This study evaluated spirometric criteria for that use. Eighty-three patients with an acute exacerbation of COPD were studied; 45 percent were admitted to the hospital while 17 percent of the patients who were discharged suffered a relapse. An FEV1 of less than 40 percent of predicted normal identified patients who required hospital admission or suffered a relapse with a sensitivity of 0.96, specificity of 0.58, and overall accuracy of 0.78. Combining clinical assessment with spirometry led to an improvement in specificity to 0.73 with a minimal decrease in sensitivity. Patients with an FEV1 of 40 percent or greater of predicted normal or no clinical evidence of respiratory distress after treatment may be safely discharged from the hospital. Patients not meeting these criteria are at high risk for relapse and should either be admitted or have further aggressive ED therapy. 