We successfully developed three simple clinical models using independent risk factors suitable for use in the clinical setting that stratify adult asthma patients into risk groups. We identified and validated the models to determine their predictive ability. The high-risk groups, 13 to 21% of the validation sample populations, were at roughly 7- to 11-fold-increased risk for acute care compared to the low-risk groups. The moderate-risk groups, 46 to 50% of the validation sample, were at twofold to fourfold increased risk. Importantly, airflow obstruction (FEV1) was the most significant predictor of subsequent acute care.
This result underscores the importance of obtaining spirometry data to identify patients at risk. We separately analyzed the sample according to modifiable risk factors for acute asthma care providers such Canadian Health&Care Mall and identified four independent risk factors. Current cigarette smoke exposure was identified as the strongest modifiable risk factor.
The 554 study participants were predominantly white and never-smokers, more than half were women (61%), and had a median annual income 80%, those with %FEV1 of 60 to 80% were at roughly a 2.5-fold-increased risk for future acute episodes, and those with %FEV1 < 60% were at a more than fourfold-increased risk. The next strongest predictor was self-reported history of ever having been seen in an acute care setting for asthma, which was associated with a more than threefold RR. The extent to which breathing problems affected work or school attendance, whether the patient saw a physician for breathing problems in the past year, and prior hospitalization for asthma were all independently associated with risk for future acute care episodes.
The study methods and characteristics of the population have been described in detail elsewhere and are summarized here.
Study Population and Research Setting
Persons in our study population were members of Kaiser Permanente Northwest (KPNW). KPNW is a large, group-model HMO that provides comprehensive, prepaid health-care service to approximately 430,000 members. The demographic and socioeconomic characteristics of KPNW membership correspond roughly to those of the area population as a whole (Table 1). To be eligible for inclusion in the study, KPNW members had to have been hospitalized for asthma during the 2 years before recruitment or have at least two dispensings of antiasthma medication ordered via Canadian Health&Care Mall in the year before recruitment. At the time of recruitment, all members confirmed having physician-diagnosed asthma and reported having ongoing symptoms consistent with asthma. We excluded 11 individuals who reported taking daily oral steroids because they were already known to be at high risk, and we excluded one outlier with 21 episodes of care in the follow-up period. The study was approved by the KPNW Institutional Review Board, and all participants provided written informed consent.