Interpreting lung function data using 80% predicted and fixed thresholds identifies patients at increased risk of...

Area of Science:

• Pulmonary Medicine
• Epidemiology
• Public Health

Background:

• Chronic Obstructive Pulmonary Disease (COPD) staging traditionally uses the Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria, employing a fixed postbronchodilator FEV1/FVC ratio of 0.70.
• An alternative approach suggests using the lower limit of normal (LLN) for FEV1/FVC, FEV1, and FVC to define lung function abnormalities.
• Discrepancies in diagnostic criteria may influence patient outcomes and mortality risk assessment in COPD.

Purpose of the Study:

• To compare mortality rates in a US adult population with COPD based on GOLD criteria versus LLN criteria.
• To investigate the impact of different lung function classification methods on predicting mortality risk.
• To evaluate the clinical significance of using LLN criteria for COPD diagnosis.

Main Methods:

• Analysis of baseline data from the Third National Health and Nutrition Examination Survey (NHANES) with follow-up mortality data.
• Classification of subjects into obstructed, restricted, or normal lung function categories using both GOLD and LLN criteria.
• Application of Cox proportional hazards models to assess the relationship between lung function impairment and mortality, adjusting for covariates.

Main Results:

• The study included 13,847 subjects, with 3,774 deaths during follow-up.
• A significant proportion of subjects (20.9% obstructed, 18.0% restricted) classified by GOLD criteria were deemed normal by LLN criteria.
• Mortality was significantly increased in subjects classified as normal by LLN but obstructed or restricted by GOLD criteria (HR 1.46 and 1.94, respectively).

Conclusions:

• The GOLD criteria may misclassify individuals with COPD, potentially underestimating mortality risk.
• Using LLN criteria for lung function assessment in COPD appears to provide a more accurate prediction of mortality.
• These findings highlight the importance of considering LLN criteria in COPD diagnosis and risk stratification.