Peak expiratory flow rate as a surrogate for forced expiratory volume in 1 second in COPD severity classification in Thailand

Abstract

Background

There are limited studies directly comparing correlation and agreement between peak expiratory flow rate (PEFR) and forced expiratory volume in 1 second (FEV ₁) for severity classification of COPD. However, clarifying the role of PEFR as a surrogate of COPD severity classification instead of FEV ₁ is essential in situations and areas where spirometry is not routinely available.

Purpose

To evaluate the agreement between FEV ₁ and PEFR using Global initiative for chronic Obstructive Lung Disease (GOLD) severity classification criteria.

Materials and methods

This cross-sectional study included stable COPD patients. Both absolute values and % predicted FEV ₁ and % predicted PEFR were obtained from the same patients at a single visit. The severity of COPD was classified according to GOLD criteria. Pearson’s correlation coefficient was used to examine the relationship between FEV ₁ and PEFR. The agreement of % predicted FEV ₁ and % predicted PEFR in assigning severity categories was calculated using Kappa statistic, and identification of the limits of agreement was by Bland–Altman analysis. Statistical significance was set at P-value <0.05.

Results

Three hundred stable COPD patients were enrolled; 195 (65.0%) male, mean age 70.4±9.4 years, and mean % predicted FEV ₁ 51.4±20.1. Both correlations between the % predicted FEV ₁ and PEFR as well as the absolute values were strongly significant ( r=0.76, P<0.001 and r=0.87, P<0.001, respectively). However, severity categories of airflow limitation based on % predicted FEV ₁ or PEFR intervals were concordant in only 179 patients (59.7%). The Kappa statistic for agreement was 0.41 (95% confidence interval, 0.34–0.48), suggesting unsatisfied agreement. The calculated limits of agreement were wide (+27.1% to −28.9%).

Conclusion

Although the correlation between FEV ₁ and PEFR measurements were strongly significant, the agreement between the two tests was unsatisfied and may influence inappropriate clinical decision making in diagnosis, severity classification, and management of COPD.