Predicting risk of airflow obstruction in primary care: Validation of the lung function questionnaire (LFQ)

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 <or=18 was selected to suggest presence of airflow obstruction with area under the receiver operating characteristic curve 0.652; sensitivity 82.6%; specificity 47.8%; 54.3% correctly classified. While the specificity of LFQ is low, its high sensitivity suggests that it can serve to identify patients who should be further assessed using spirometry. Our results confirm the screening accuracy of the LFQ, a simple and effective tool to facilitate early recognition and diagnosis of COPD.