Predicted lower limit of normal reduces misclassification risk of airflow limitation in asymptomatic elderly...

It remains controversial what better defines abnormal lung function at the extremes of age. This study aimed to establish new spirometric reference equations for residents in Jinan and compare the most accepted two spirometric definitions of chronic obstructive pulmonary disease (COPD)-a fixed post-bronchodilator ratio of forced expiratory volume in one second to forced vital capacity (FEV1/FVC) below 70% vs. FEV1/FVC < lower limit of normal (LLN)-in an elderly population (age ≥60 years).

Among 10 002 cases, only never-smokers who had no respiratory symptoms or diagnoses of cardiopulmonary diseases and whose lung function measurements strictly followed the American Thoracic Society guidelines, were included in the statistical analysis. For each gender, prediction equations of FEV1, FVC, FEV1/FVC and corresponding LLN values were developed using multiple regression models.

In this cross-sectional study, spirometric reference values were statistically derived from a sample of 1328 healthy never-smokers (672 males, 656 females), age 56-84 years. As expected, age and height were the main predictors for all lung function parameters. Using the two spirometric definitions, the number of pulmonary function test results interpreted as obstructed varied markedly in the elderly population for both genders (males: χ(2) = 19.59, P < 0.01; females: χ(2) = 5.67, P = 0.017).

The Global Initiative for Chronic Obstructive Lung Disease (GOLD) criterion probably leads to overdiagnosis in asymptomatic elderly never-smokers. Our study suggests that the predicted LLN values will reduce the misclassification risk instead. However, cohort studies are urgently needed for clinical validation.