Improving accuracy of International Classification of Diseases codes for venous thromboembolism in administrative data

Background: Increasingly, clinicians and researchers are using administrative data for clinical and outcomes research. However, they continue to question the accuracy of using International Classification of Diseases 9th Revision (ICD-9) codes alone to capture diagnoses, especially venous thromboembolism (VTE), in administrative data.

Objectives: We tested the hypothesis that incorporation of treatment data and/or common procedural terminology (CPT) codes could improve accuracy of administrative data in detecting VTE. Research Design Using the Veterans Affairs Central Cancer Registry, we compared three competing algorithms by performing three cross-sectional studies. Algorithm 1 identified patients by ICD-9 codes alone. Algorithm 2 required VTE treatment in addition to ICD-9 codes. Algorithm 3 required a VTE diagnostic CPT code in addition to treatment and ICD-9 criteria.

Results: The accuracy of ICD-9 codes alone for detection of VTE was marginal, with a PPV of 72%. The PPV was improved to 91% after addition of treatment data (algorithm 2). As compared to algorithm 2, addition of CPT codes (algorithm 3) did not significantly increase the accuracy of detecting VTE (PPV 92%), but decreased sensitivity from 72% to 67%.

Conclusions: Accuracy of VTE detection significantly improved with addition of treatment data to ICD-9 codes. This approach should facilitate use of administrative data to assess the incidence, epidemiology, and outcomes of VTE.