title: Development and validation of an ankle brachial index risk model for the prediction of cardiovascular events.
abstract: BACKGROUND
  The ankle brachial index (ABI) is related to risk of cardiovascular events independent of the Framingham risk score (FRS). The aim of this study was to develop and evaluate a risk model for cardiovascular events incorporating the ABI and FRS.
  
  
  METHODS
  An analysis of participant data from 18 cohorts in which 24,375 men and 20,377 women free of coronary heart disease had ABI measured and were followed up for events.
  
  
  METHODS
  Subjects were divided into a development and internal validation dataset and an external validation dataset. Two models, comprising FRS and FRS + ABI, were fitted for the primary outcome of major coronary events.
  
  
  RESULTS
  In predicting events in the external validation dataset, C-index for the FRS was 0.672 (95% CI 0.599 to 0.737) in men and 0.578 (95% CI 0.492 to 0.661) in women. The FRS + ABI led to a small increase in C-index in men to 0.685 (95% CI 0.612 to 0.749) and large increase in women to 0.690 (95% CI 0.605 to 0.764) with net reclassification improvement (NRI) of 4.3% (95% CI 0.0 to 7.6%, p = 0.050) and 9.6% (95% CI 6.1 to 16.4%, p < 0.001), respectively. Restricting the FRS + ABI model to those with FRS intermediate 10-year risk of 10 to 19% resulted in higher NRI of 15.9% (95% CI 6.1 to 20.6%, p < 0.001) in men and 23.3% (95% CI 13.8 to 62.5%, p = 0.002) in women. However, incorporating ABI in an improved newly fitted risk factor model had a nonsignificant effect: NRI 2.0% (95% CI 2.3 to 4.2%, p = 0.567) in men and 1.1% (95% CI 1.9 to 4.0%, p = 0.483) in women.
  
  
  CONCLUSIONS
  An ABI risk model may improve prediction especially in individuals at intermediate risk and when performance of the base risk factor model is modest.
authors.affiliation: Centre for Population Health Sciences, University of Edinburgh, Edinburgh, UK.
authors.forename: F G R
authors.initials: FG
authors.lastname: Fowkes
authors.forename: G D
authors.initials: GD
authors.lastname: Murray
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authors.forename: C D A
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authors.lastname: Stehouwer
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authors.initials: MM
authors.lastname: McDermott
authors.forename: H E J H
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authors.lastname: Stoffers
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authors.lastname: Knottnerus
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authors.lastname: Ogren
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authors.lastname: Hedblad
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authors.lastname: Koenig
authors.forename: C
authors.initials: C
authors.lastname: Meisinger
authors.forename: J A
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authors.lastname: Cauley
authors.forename: Oh
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authors.lastname: Franco
authors.forename: M G M
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authors.lastname: Hunink
authors.forename: A
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authors.lastname: Hofman
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authors.initials: JC
authors.lastname: Witteman
authors.forename: M H
authors.initials: MH
authors.lastname: Criqui
authors.forename: R D
authors.initials: RD
authors.lastname: Langer
authors.forename: W R
authors.initials: WR
authors.lastname: Hiatt
authors.forename: R F
authors.initials: RF
authors.lastname: Hamman
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D055109:Ankle Brachial Index; D002318:Cardiovascular Diseases / Q000175:diagnosis* / Q000453:epidemiology* / Q000503:physiopathology; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D011237:Predictive Value of Tests; D011379:Prognosis; D015203:Reproducibility of Results; D018570:Risk Assessment; D012307:Risk Factors; D012737:Sex Factors; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D044465:White People; D055815:Young Adult
keywords: Ankle brachial index; cardiovascular diseases; risk assessment