Airflow Obstruction Categorization Methods and Mortality.

RATIONALE

Current guidelines recommend using forced expiratory volume in 1 second (FEV) % predicted to categorize the severity of airflow obstruction. There are limitations to using FEV % predicted for this purpose, including bias associated with demographic factors and the inability to correct for "lung size." Other methods for grading the severity of airflow obstruction have been proposed to address these limitations.

OBJECTIVES

Our objectives were to categorize airflow obstruction severity using these methods and then determine which method results in a categorization most closely associated with mortality.

METHODS

Study subjects were patients aged 40-80 years tested in our pulmonary function test laboratories in the period 2002 to 2013 with airflow obstruction based on an FEV/forced vital capacity (FVC) less than the lower limit of normal. Categorization of airflow obstruction severity was determined using four methods: FEV % predicted; FEV % predicted adjusted by FVC % predicted; FEV/FVC confidence interval approach; and FEV z-scores. Receiver operating characteristic curve analysis was used to determine which categorization method best predicts 5-year survival.

RESULTS

We identified 2,000 patients with airflow obstruction. Important differences in the categorization of airflow obstruction severity were observed using the different methods. More patients were categorized as having severe obstruction using FEV % predicted and FEV z-scores compared with FEV % predicted adjusted by FVC % predicted and FEV/FVC confidence interval approach. FEV % predicted was the best predictor of 5-year survival among the four methods studied.

CONCLUSIONS

In our study, categorizing airflow obstruction severity using FEV % predicted best predicted 5-year survival. This validates the current guideline recommendation that FEV % predicted be used to categorize the severity of airflow obstruction.