The Lung Function Questionnaire (LFQ) is being developed as a case finding tool to identify patients who are appropriate for spirometry testing to confirm the diagnosis of chronic obstructive pulmonary disease (COPD). The cross-sectional study reported herein was conducted to validate the LFQ, to identify item-response scales associated with the best accuracy, and to determine the impact on accuracy of the addition of another item on activity limitations (AL). Patients >or= 40 years old seen at 2 primary care offices completed the LFQ, a demographic questionnaire followed by spirometry. Of the 837 evaluable patients, 18.6% had airflow obstruction (forced expiratory volume in 1 s/forced vital capacity [FEV(1)/FVC] < 0.70). The 5 items (age, wheeze, dyspnea, smoking, and cough) previously identified in initial LFQ development predicted airflow obstruction and showed good evidence of screening accuracy. Screening accuracy was significantly better with 5-point ordinal item-response scales (78%) than binary (yes/no) item-response scales (74%)(p < 0.05). Screening accuracy was good regardless of whether airflow obstruction was defined as FEV(1)/FVC < 0.70 or FEV(1)/FVC < 0.70 and FEV(1) < 80% of predicted. Based on