title: Subtypes of asthma based on asthma control and severity: a latent class analysis.
abstract: Asthma subtyping is a complex new field of study. Usually both etiological and outcome factors of asthma have been used simultaneously for subtyping thus making the interpretation of the results difficult. Identification of subtypes of asthma based on questionnaire data only will be useful for both treatment of asthma and for research. Our objective was to identify asthma subtypes that capture both asthma control and severity based on easily accessible variables.
  
  
  
  We applied latent class analysis for the 1995 adult asthmatics, 692 men and 1303 women, of the Northern Finnish Asthma Study (NoFAS). The classifying variables included use of asthma medication within the last 12 months, St. George's Respiratory Questionnaire score, and asthma-related healthcare use within the last 12 months. Covariates adjusted for included COPD, allergic rhinitis/allergic eczema, BMI, age and sex. All information was based on self-administered questionnaires.
  
  
  
  We identified four subtypes for women: Controlled, mild asthma (41% of participants); Partly controlled, moderate asthma (24%); Uncontrolled asthma, unknown severity (26%), and Uncontrolled, severe asthma (9%). For men we identified three subtypes: Controlled, mild asthma (31%); Poorly controlled asthma, unknown severity (53%); and Partly controlled, severe asthma (17%). For almost 96% of the subjects this subtyping was accurate. The covariates fitted in the model were based on clinical judgment and were good predictors of class membership.
  
  
  
  Our results show that it is possible to form meaningful and accurate asthma subtypes based on questionnaire data, and that separate classification should be applied for men and women.
authors.affiliation: Center for Environmental and Respiratory Health Research (CERH), University of Oulu, PO Box 5000, FI-90014, Oulu, Finland.|Medical Research Center Oulu (MRC Oulu), Oulu, Finland.
authors.forename: Elina M S
authors.initials: EM
authors.lastname: Mäkikyrö
authors.affiliation: Center for Environmental and Respiratory Health Research (CERH), University of Oulu, PO Box 5000, FI-90014, Oulu, Finland.|Medical Research Center Oulu (MRC Oulu), Oulu, Finland.
authors.forename: Maritta S
authors.initials: MS
authors.lastname: Jaakkola
authors.affiliation: Center for Environmental and Respiratory Health Research (CERH), University of Oulu, PO Box 5000, FI-90014, Oulu, Finland. Jouni.jaakkola@oulu.fi.|Medical Research Center Oulu (MRC Oulu), Oulu, Finland. Jouni.jaakkola@oulu.fi.
authors.forename: Jouni J K
authors.initials: JJ
authors.lastname: Jaakkola
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001249:Asthma / Q000145:classification* / Q000175:diagnosis* / Q000453:epidemiology; D005387:Finland / Q000453:epidemiology; D006801:Humans; D008875:Middle Aged; D015999:Multivariate Analysis; D015995:Prevalence; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D017678:Sex Distribution; D011795:Surveys and Questionnaires; D063189:Symptom Assessment / Q000379:methods*; D055815:Young Adult
keywords: Asthma; Asthma control; Asthma severity; Asthma subtypes; Determinant; Epidemiologic study; Latent class analysis; Risk factor