Assessing symptoms and peak expiratory flow rate as predictors of asthma exacerbations

Abstract

Objective: To investigate peak expiratory flow rate (PEFR) and quality of life scores for their ability to predict exacerbations of asthma.

Participants and methods: We identified adults who received oral or inhaled asthma medications from 36 community drugstores. We administered the McMaster Asthma Quality of Life Questionnaire (AQLQ) and measured PEFR, defining "red zone" (highest risk) as a PEFR < 50% of each patient's expected value based on gender, age, and height. We identified asthma exacerbations (breathing-related emergency department visits and hospitalizations) within 4 and 12 months after enrollment and used proportional hazards regression to assess the ability of PEFR and AQLQ scores to predict exacerbations, controlling for clinical and demographic factors.

Results: A red zone PEFR was a significant univariable predictor of exacerbations within 12 months (hazard ratio [HR], 1.8; 95% confidence interval [CI], 1.1 to 3.0; P =.027). However, neither a red zone PEFR, the raw PEFR, or percent of predicted maximal PEFR were significantly predictive when controlling for AQLQ scores, clinical characteristics, or demographic data (P >.2). However, the 4 subscales of the AQLQ were each significant univariable and multivariable predictors of asthma exacerbations. For example, the overall AQLQ scale had a multivariable HR of 0.63 (95% CI, 0.46 to 0.87; P =.005) for exacerbations occurring within 4 months and 0.66 (95% CI, 0.54 to 0.82; P <.001) within 12 months.

Conclusions: PEFR added no predictive information to that contained in AQLQ scores and clinical and demographic data. These results support the National Institutes of Health asthma guidelines' recommendation for routinely assessing symptoms but not PEFR.

FIGURE 1

Time to first asthma-related emergency visit or hospitalization by overall quality of life score. Plot is a survival curve. The solid line represents patients with an overall scale score less than 4 (n = 212). The dotted line represents patients with overall scale scores of 4.0 to 5.0 inclusive (n = 229). The broken line represents patients with an overall scale score of greater than 5 (n = 219). Censored observations are indicated by “+ ”.