The utility of peak flow, symptom scores, and β-agonist use as outcome measures in asthma clinical research

Study objectives: Several methods of utilizing peak expiratory flow (PEF) and other markers of disease activity have been suggested as useful in the management of asthma. It remains unclear, however, as to which surrogate markers of disease status are discriminative indicators of treatment failure, suitable for use in clinical trials. Design: We analyzed the operating characteristics of 66 surrogate markers of treatment failure using a receiver operating characteristic (ROC) curve analysis. Participants: Information regarding FEV₁, symptoms, β2-agonist use, and PEF was available from 313 subjects previously enrolled in two Asthma Clinical Research Network trials, in which 71 treatment failures occurred (defined by a 20% fall in FEV₁ from baseline). Interventions: None. Measurements and results: None of the measures had an acceptable ability to discriminate subjects with a ≥ 20% fall in FEV₁ from those without, regardless of the duration of the period of analysis or the criteria for test positivity employed. Areas under the ROC curves generated ranged from 0.51 to 0.79, but none were statistically superior. Sensitivity and specificity combinations were generally poor at all cutoff values; true-positive rates could not be raised without unacceptably elevating false-positive rates concurrently. Conclusions: Studies that seek to detect treatment failure defined by a significant fall in FEV₁ should not use such individual surrogate measures to estimate disease severity.