A Spirometry-Based Algorithm To Direct Lung Function Testing in the Pulmonary Function Laboratory

Objective: To design a spirometry-based algorithm to predict pulmonary restrictive impairment and reduce the number of patients undergoing unnecessary lung volume testing. Design: Two prospective studies of 259 consecutive patients and 265 consecutive patients used to derive and validate the algorithm, respectively. Setting: A pulmonary function laboratory of a tertiary care hospital. Patients: Consecutive adults referred to the laboratory for lung volume measurements and spirometry. Measurements: The sensitivity of the algorithm for predicting pulmonary restriction and the cost savings associated with its use. Results: Total lung capacity correlated strongly with FVC (r 0.66) and showed an inverse correlation with the FEV1/FVC ratio (r 0.41). According to the algorithm, only patients with an FVC < 85 % of predicted and an FEV1/FVC ratio> 55 % required lung volume measurements following spirometry. The algorithm had a high sensitivity for predicting restriction and a high negative predictive value (NPV) for excluding restriction (sensitivity, 96%; NPV, 98%). The diagnostic properties of the algorithm were reproducible in the validation study. Application of the algorithm would eliminate the need for lung volume testing in 48 to 49 % of patients referred to the pulmonary function test (PFT) laboratory, reducing costs by 33%. Conclusions: A spirometry-based algorithm accurately excludes pulmonary restriction and reduces unnecessary lung volume testing in the PFT laboratory almost in half. (CHEST 2003; 123:1939–1946) Key words: diagnosis; lung volumes; pulmonary function test; restriction; spirometr