title: Predicting future risk of asthma exacerbations using individual conditional probabilities.
abstract: BACKGROUND
  Determination of future risk of exacerbations is a key issue in the management of asthma. We previously developed a method to calculate conditional probabilities (π) of future decreases in lung function by using the daily fluctuations in peak expiratory flow (PEF).
  
  
  OBJECTIVE
  We aimed to extend calculation of π values to individual patients, validated by using electronically recorded data from 2 past clinical trials.
  
  
  METHODS
  Twice-daily PEF data were analyzed from 78 patients with severe (study A) and 61 patients with poorly controlled (study B) asthma. For each patient, the π value was calculated from 5000 PEF data points simulated based on the correlation and distribution properties of observed PEF. Given an initial PEF, the π value was defined as the probability of a decrease in PEF to less than 80% of predicted value on 2 consecutive days within a month. These probabilities were then compared with actual occurrences of such events and clinically defined exacerbations within the following month.
  
  
  RESULTS
  π Values were related to actual occurrences of decreases in PEF (adjusted R(2) > 0.800 for both studies). Every increase of 10% in π value was associated with an odds ratio of having a future exacerbation of 1.24 (95% CI, 1.07-1.43) for study A and 1.13 (95% CI, 1.02-1.26) for study B, with better sensitivity and specificity than clinic-measured FEV(1).
  
  
  CONCLUSIONS
  These results from 2 independent datasets with differing asthmatic populations and differing exacerbation criteria provide support that clinically relevant quantification of individual future risk of exacerbations is possible.
authors.affiliation: Division of Respiratory Medicine, Department of Paediatrics, Inselspital and University of Bern, Bern, Switzerland.
authors.forename: Cindy
authors.initials: C
authors.lastname: Thamrin
authors.forename: Joel
authors.initials: J
authors.lastname: Zindel
authors.forename: Regula
authors.initials: R
authors.lastname: Nydegger
authors.forename: Helen K
authors.initials: HK
authors.lastname: Reddel
authors.forename: Pascal
authors.initials: P
authors.lastname: Chanez
authors.forename: Sally E
authors.initials: SE
authors.lastname: Wenzel
authors.forename: Susan
authors.initials: S
authors.lastname: FitzPatrick
authors.forename: Rosemary A
authors.initials: RA
authors.lastname: Watt
authors.forename: Béla
authors.initials: B
authors.lastname: Suki
authors.forename: Urs
authors.initials: U
authors.lastname: Frey
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001249:Asthma / Q000209:etiology* / Q000503:physiopathology* / Q000628:therapy; D018450:Disease Progression; D015987:Effect Modifier, Epidemiologic; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010366:Peak Expiratory Flow Rate; D011237:Predictive Value of Tests; D011336:Probability; D012008:Recurrence; D012189:Retrospective Studies; D012307:Risk Factors; D055815:Young Adult