title: Prediction of risk of recurrence of venous thromboembolism following treatment for a first unprovoked venous thromboembolism: systematic review, prognostic model and clinical decision rule, and economic evaluation.
abstract: BACKGROUND
  Unprovoked first venous thromboembolism (VTE) is defined as VTE in the absence of a temporary provoking factor such as surgery, immobility and other temporary factors. Recurrent VTE in unprovoked patients is highly prevalent, but easily preventable with oral anticoagulant (OAC) therapy. The unprovoked population is highly heterogeneous in terms of risk of recurrent VTE.
  
  
  OBJECTIVE
  The first aim of the project is to review existing prognostic models which stratify individuals by their recurrence risk, therefore potentially allowing tailored treatment strategies. The second aim is to enhance the existing research in this field, by developing and externally validating a new prognostic model for individual risk prediction, using a pooled database containing individual patient data (IPD) from several studies. The final aim is to assess the economic cost-effectiveness of the proposed prognostic model if it is used as a decision rule for resuming OAC therapy, compared with current standard treatment strategies.
  
  
  METHODS
  Standard systematic review methodology was used to identify relevant prognostic model development, validation and cost-effectiveness studies. Bibliographic databases (including MEDLINE, EMBASE and The Cochrane Library) were searched using terms relating to the clinical area and prognosis. Reviewing was undertaken by two reviewers independently using pre-defined criteria. Included full-text articles were data extracted and quality assessed. Critical appraisal of included full texts was undertaken and comparisons made of model performance. A prognostic model was developed using IPD from the pooled database of seven trials. A novel internal-external cross-validation (IECV) approach was used to develop and validate a prognostic model, with external validation undertaken in each of the trials iteratively. Given good performance in the IECV approach, a final model was developed using all trials data. A Markov patient-level simulation was used to consider the economic cost-effectiveness of using a decision rule (based on the prognostic model) to decide on resumption of OAC therapy (or not).
  
  
  RESULTS
  Three full-text articles were identified by the systematic review. Critical appraisal identified methodological and applicability issues; in particular, all three existing models did not have external validation. To address this, new prognostic models were sought with external validation. Two potential models were considered: one for use at cessation of therapy (pre D-dimer), and one for use after cessation of therapy (post D-dimer). Model performance measured in the external validation trials showed strong calibration performance for both models. The post D-dimer model performed substantially better in terms of discrimination (c = 0.69), better separating high- and low-risk patients. The economic evaluation identified that a decision rule based on the final post D-dimer model may be cost-effective for patients with predicted risk of recurrence of over 8% annually; this suggests continued therapy for patients with predicted risks ≥ 8% and cessation of therapy otherwise.
  
  
  CONCLUSIONS
  The post D-dimer model performed strongly and could be useful to predict individuals' risk of recurrence at any time up to 2-3 years, thereby aiding patient counselling and treatment decisions. A decision rule using this model may be cost-effective for informing clinical judgement and patient opinion in treatment decisions. Further research may investigate new predictors to enhance model performance and aim to further externally validate to confirm performance in new, non-trial populations. Finally, it is essential that further research is conducted to develop a model predicting bleeding risk on therapy, to manage the balance between the risks of recurrence and bleeding.
  
  
  BACKGROUND
  This study is registered as PROSPERO CRD42013003494.
  
  
  BACKGROUND
  The National Institute for Health Research Health Technology Assessment programme.
authors.affiliation: Public Health, Epidemiology and Biostatistics, School of Health and Population Sciences, University of Birmingham, Birmingham, UK.|Research Institute of Primary Care and Health Sciences, Keele University, Staffordshire, UK.
authors.forename: Joie
authors.initials: J
authors.lastname: Ensor
authors.affiliation: Public Health, Epidemiology and Biostatistics, School of Health and Population Sciences, University of Birmingham, Birmingham, UK.|Research Institute of Primary Care and Health Sciences, Keele University, Staffordshire, UK.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Riley
authors.affiliation: Health Economics, School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
authors.forename: Sue
authors.initials: S
authors.lastname: Jowett
authors.affiliation: Health Economics, School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Monahan
authors.affiliation: Public Health, Epidemiology and Biostatistics, School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
authors.forename: Kym Ie
authors.initials: KIe
authors.lastname: Snell
authors.affiliation: Public Health, Epidemiology and Biostatistics, School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
authors.forename: Susan
authors.initials: S
authors.lastname: Bayliss
authors.affiliation: Public Health, Epidemiology and Biostatistics, School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
authors.forename: David
authors.initials: D
authors.lastname: Moore
authors.affiliation: Primary Care Clinical Sciences, School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
authors.forename: David
authors.initials: D
authors.lastname: Fitzmaurice
mesh_terms: D000925:Anticoagulants / Q000191:economics / Q000627:therapeutic use*; D003362:Cost-Benefit Analysis; D020000:Decision Support Systems, Clinical; D006801:Humans; D011379:Prognosis; D012307:Risk Factors; D055502:Secondary Prevention; D013673:Technology Assessment, Biomedical; D054556:Venous Thromboembolism / Q000188:drug therapy* / Q000517:prevention & control
chemical_list: D000925:Anticoagulants