title: Predictors of late asthmatic response. Logistic regression and classification tree analyses.
abstract: To identify predictors of the late asthmatic response (LAR), we reviewed data from 60 asthmatic subjects who had undergone allergen challenge over the past 5 yr (33 females, age 31.4 +/- 6.7 yr [mean +/- SD], FEV(1) 90% +/- 14% predicted). Variables considered likely predictors of LAR included baseline FEV(1), PC(20) methacholine (PC(20)), sputum eosinophil percent, and the decrease in FEV(1) within 20 min of allergen challenge. A LAR (FEV(1) >/= 15% fall between 3 and 7 h after challenge) was documented in 57% of subjects. A variety of logistic regression methods revealed a significant inverse association between LAR and PC(20) (odds ratio [OR] = 0.14 [95% CI = 0.03-0.66]) and a positive association between LAR and the decrease in FEV(1) at 20 min (OR = 1.18 [1.04 -1.33]). Classification tree analysis revealed that a threshold of 0.25 mg/ml for PC(20) was most predictive of LAR; LAR developed in 87% of those with PC(20) </= 0.25 mg/ml (n = 23) and in 38% of those with PC(20) > 0.25 mg/ml (n = 37). Notably, in subjects with PC(20) > 0.25 mg/ml, the incidence of LAR increased from 38% to 57% if the allergen-induced decline in FEV(1) at 20 min was >/= 27%. Surprisingly, baseline FEV(1) and percent eosinophils in induced sputum were not significantly associated with LAR. We conclude that a threshold value of 0.25 mg/ml for PC(20) methacholine is a good predictor of LAR. Measuring the PC(20) methacholine may be useful as a screening method to improve the efficiency of identifying asthmatic subjects with a LAR.
authors.affiliation: Cardiovascular Research Institute, Department of Medicine, University of California at San Francisco, San Francisco, California 94143-0111, USA.
authors.forename: P C
authors.initials: PC
authors.lastname: Avila
authors.forename: M R
authors.initials: MR
authors.lastname: Segal
authors.forename: H H
authors.initials: HH
authors.lastname: Wong
authors.forename: H A
authors.initials: HA
authors.lastname: Boushey
authors.forename: J V
authors.initials: JV
authors.lastname: Fahy
mesh_terms: D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology; D016535:Bronchial Hyperreactivity / Q000175:diagnosis* / Q000503:physiopathology; D001985:Bronchial Provocation Tests / Q000706:statistics & numerical data; D004804:Eosinophils / Q000276:immunology; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D006968:Hypersensitivity, Delayed / Q000175:diagnosis* / Q000503:physiopathology; D007958:Leukocyte Count; D008297:Male; D011237:Predictive Value of Tests; D012044:Regression Analysis; D012130:Respiratory Hypersensitivity / Q000175:diagnosis* / Q000503:physiopathology