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.

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Published in International Journal of COPD, v. 11, issue 1, p. 369-379.

© 2016 Lee et al.

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This study was supported by a grant of the Korea Healthcare Technology R&D Project, Ministry for Health and Welfare, Republic of Korea (A102065 and HI10C2020) and the Obstructive Lung Disease Research Foundation (www.oldrf.org). This study was also supported by grants from the Asan Institute for Life Sciences (14-306).