Development of a spirometry T-score in the general population

Abstract

Sei Won Lee,1 Hyun Kuk Kim,2 Seunghee Baek,3 Ji-Ye Jung,4 Young Sam Kim,4 Jae Seung Lee,1 Sang-Do Lee,1 David M Mannino,5 Yeon-Mok Oh1 1Department of Pulmonary and Critical Care Medicine, Clinical Research Center for Chronic Obstructive Airway Diseases, Asan Medical Center, University of Ulsan College of Medicine, Seoul, 2Department of Pulmonary and Critical Care Medicine, Haeundae Paik Hospital, Inje University College of Medicine, Busan, 3Department of Clinical Epidemiology and Biostatistics, Asan Medical Center, University of Ulsan College of Medicine, Seoul, 4Division of Pulmonary, Department of Internal Medicine, Institute of Chest Disease, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea; 5Department of Preventive Medicine and Environmental Health, University of Kentucky College of Public Health, Lexington, KY, USA Background and objective: Spirometry values may be expressed as T-scores in standard deviation units relative to a reference in a young, normal population as an analogy to the T-score for bone mineral density. This study was performed to develop the spirometry T-score. Methods: T-scores were calculated from lambda-mu-sigma-derived Z-scores using a young, normal age reference. Three outcomes of all-cause death, respiratory death, and COPD death were evaluated in 9,101 US subjects followed for 10 years; an outcome of COPD-related health care utilization (COPD utilization) was evaluated in 1,894 Korean subjects followed for 4 years. Results: The probability of all-cause death appeared to remain nearly zero until -1 of forced expiratory volume in 1 second (FEV1) T-score but increased steeply where FEV1 T-score reached below -2.5. Survival curves for all-cause death, respiratory death, COPD death, and COPD utilization differed significantly among the groups when stratified by FEV1 T-score (P<0.001). The adjusted hazard ratios of the FEV1 T-score for the four outcomes were 0.54 (95% confidence interval, 0.48–0.60), 0.43 (95% CI: 0.37–0.50), 0.30 (95% CI: 0.24–0.37), and 0.69 (95% CI: 0.59–0.81), respectively, adjusting for covariates (P<0.001). Conclusion: The spirometry T-score could predict all-cause death, respiratory death, COPD death, and COPD utilization. Keywords: spirometry, T-score, COPD

Keywords

• Spirometry
• T-score
• COPD (chronic obstructive pulmonary disease)