The validity of the diagnosis of heart failure (I50.0-I50.9) in the Danish National Patient Register.

INTRODUCTION: National discharge registers are important and cost-effective data sources for administrative and research purposes, but their value depends much on the validity of the registered data. The objective of this study was to assess the validity of heart failure (HF) diagnoses (ICD10: I50.0-I50.9) in the Danish National Patient Register (DNPR).

METHODS: We reviewed medical records from a random sample of 500 patients with either a primary or a secondary discharge diagnosis of HF registered in the DNPR from any department in Northern Denmark in 2007. We noted symptoms, objective signs, diagnostic imaging and biomarkers and used the European Society of Cardiology definition of HF to categorise patients into definite, probable or non-
verified HF.

RESULTS: We classified 305 patients as having definite HF and 113 patients as having probable HF. The remaining cases were classified as non-verified HF. Thus, the positive predictive value (PPV) for definite and probable HF was 83.6% (95% confidence interval (CI): 80.1-86.7%).
The PPV increased to 88.0% (95% CI: 84.4-91.0%) when we restricted analyses to primary diagnoses and to 95.2% (95% CI: 89.2-98.4%) when we restricted analyses to HF diagnoses established at cardiology units.

CONCLUSIONS: The HF diagnoses (I50.0-I50.9) in the DNPR should be used with caution if validation is not possible. However, restricting analyses to patients registered with a primary diagnosis of HF or patients discharged from cardiology units may be a useful alternative in population-based studies.

FUNDING: none.

TRIAL REGISTRATION: not relevant.