Validity of The Danish National Chronic Myeloid Neoplasia Registry

Purpose: Myeloproliferative neoplasms (MPN) are rare hematological malignancies with long survival, making real-world evidence essential to complement clinical trial data. The Danish National Chronic Myeloid Neoplasia Registry (DMR) captures nearly all MPN patients nationwide, but its validity has not been systematically evaluated. We aimed to validate key clinical variables in the DMR through a nationwide audit. Methods: We sampled DMR entries from 372 persons registered with essential thrombocythemia (ET), polycythemia vera (PV), primary myelofibrosis (PMF), prefibrotic myelofibrosis (preMF), or unclassifiable MPN (MPN-U) between 2017 and 2021 across all regions of Denmark. We validated eight main variables, including 27 subordinate variables of clinical importance from the DMR, against electronic health records using standardized audit procedures. Positive predictive value (PPV), negative predictive value (NPV), sensitivity, specificity, and accuracy were calculated. Results: Overall, the DMR showed mostly high PPV and intermediate/high NPV values. PPV was high for core diagnostic, treatment and comorbidity variables: ET (0.91), PV (0.95) and PMF (0.97), date of diagnosis (0.97), splenomegaly (0.98), JAK2 V617F (0.97), CALR (0.92), hypertension (0.93), hyperlipidemia (0.90), diabetes (0.97), and common treatments (phlebotomy, hydroxyurea, interferon, ruxolitinib ≥ .93). Intermediate PPV was observed for diagnoses of preMF (0.78) and MPN-U (0.77), and for the remaining comorbidity variables (0.75– 0.85). Most misclassifications arose from false negatives, reflecting the automatic imputation of negative (no) for missing values for selected variables in the DMR which resulted in lower sensitivity and high PPV/specificity. Conclusion: The DMR demonstrates high validity for several clinically relevant variables and constitutes a reliable source of real-world data in MPN research and therefore, crosslinking registry variables with other data sources may enable robust epidemiological studies and unprecedented precision in real-world evidence for MPN patients. Nevertheless, variable documentation and data quality must be critically assessed to account for changes in data entry practices across time periods. Keywords: myeloproliferative disorders/epidemiology, registries/standards, data accuracy, medical record linkage, real-world evidence, Epidemiology