J Am Med Inform Assoc doi:10.1136/amiajnl-2011-000782
  • Research and applications

Patient characteristics associated with venous thromboembolic events: a cohort study using pooled electronic health record data

  1. Anil K Jain4,7
  1. 1Department of Information Services, The MetroHealth System, Cleveland, Ohio, USA
  2. 2Departments of Internal Medicine, Pediatrics, Epidemiology, and Biostatistics, Case Western Reserve University, Cleveland, Ohio, USA
  3. 3The Center for Clinical Informatics Research and Education, The MetroHealth System, Cleveland, Ohio, USA
  4. 4Explorys Inc., Cleveland, Ohio, USA
  5. 5Departments of Medicine, Epidemiology and Biostatistics, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA
  6. 6Center for Health Care Research and Policy, The MetroHealth System, Case Western Reserve University, Cleveland, Ohio, USA
  7. 7Department of Internal Medicine, Cleveland Clinic, Cleveland, Ohio, USA
  1. Correspondence to Dr David C Kaelber, Case Western Reserve University, 3158 Kingsley Road, Shaker Heights, OH 44122, USA; david.kaelber{at}
  1. Contributors Conception and design: WF, JG, AJ and DCK. Analysis and interpretation of data: WF, JG and DCK. Drafting of manuscript: WF, JG and DCK. Critical revision of manuscript for important intellectual content: WF, JG, AJ, DCK and TL. Statistical analysis: WF, JG and TL. WF, JG, AJ and DCK had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

  • Received 18 December 2011
  • Accepted 31 May 2012
  • Published Online First 3 July 2012


Objective To demonstrate the potential of de-identified clinical data from multiple healthcare systems using different electronic health records (EHR) to be efficiently used for very large retrospective cohort studies.

Materials and methods Data of 959 030 patients, pooled from multiple different healthcare systems with distinct EHR, were obtained. Data were standardized and normalized using common ontologies, searchable through a HIPAA-compliant, patient de-identified web application (Explore; Explorys Inc). Patients were 26 years or older seen in multiple healthcare systems from 1999 to 2011 with data from EHR.

Results Comparing obese, tall subjects with normal body mass index, short subjects, the venous thromboembolic events (VTE) OR was 1.83 (95% CI 1.76 to 1.91) for women and 1.21 (1.10 to 1.32) for men. Weight had more effect then height on VTE. Compared with Caucasian, Hispanic/Latino subjects had a much lower risk of VTE (female OR 0.47, 0.41 to 0.55; male OR 0.24, 0.20 to 0.28) and African-Americans a substantially higher risk (female OR 1.83, 1.76 to 1.91; male OR 1.58, 1.50 to 1.66). This 13-year retrospective study of almost one million patients was performed over approximately 125 h in 11 weeks, part time by the five authors.

Discussion As research informatics tools develop and more clinical data become available in EHR, it is important to study and understand unique opportunities for clinical research informatics to transform the scale and resources needed to perform certain types of clinical research.

Conclusions With the right clinical research informatics tools and EHR data, some types of very large cohort studies can be completed with minimal resources.


  • Competing interests DCK is the Chief Medical Informatics Officer of the MetroHealth System, which is an early participant in the Explorys network. Neither DCK nor the MetroHealth System has any direct financial ties to Explorys Inc. In exchange for contributing de-identified data to the Explorys network, the MetroHealth System receives access to the Explorys Population Explorer tool, which was used to conduct this study. JG and WF are Explorys employees who participated in this research and did not receive additional compensation for this study. AJ is the Senior-Vice President and Chief Medical Information Officer of Explorys Inc. and in addition to receiving salary, holds a financial interest in Explorys Inc. TL has no financial ties to Explorys Inc. None of the authors received funding directly to support this study.

  • Ethics approval The authors approached the MetroHealth System institutional review board to discuss this study with them and they indicated that they did not deem it as human studies research (because only de-identified, aggregate data were used).

  • Provenance and peer review Not commissioned; externally peer reviewed.

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