Agreement between self-reported and register-based cardiovascular events among Danish breast cancer survivors

We examined the degree of over- and under-reporting of cardiovascular diseases (CVDs) among female breast cancer survivors comparing self-reports to diagnostic codes from the Danish National Patient Register (NPR). The study comprised 357 Danish breast cancer patients from the WECARE study who completed a telephone interview concerning CVDs. Disease diagnoses for these women were obtained from the NPR. Agreement was calculated as the number of diagnoses that were both self-reported and in the NPR divided by (1) number of self-reported diagnoses (over-reporting) or (2) number of diagnoses in the NPR (under-reporting). In total, 68 women reported 96 specific cardiovascular outcomes of which 56 (58%) were found in the NPR. Ninety cardiovascular diagnoses were found in the NPR of which 56 (62%) were specifically reported at the interview. There was 80% agreement as to the occurrence of a cardiovascular diagnosis overall. Of 289 women reporting no CVD, 273 (94%) had no diagnoses in the NPR. Breast cancer survivors seem to report absence of CVD accurately, but they both over-report and under-report specific cardiovascular diagnoses. Using a broader definition of CVDs improves the agreement between self-reported and NPR data. Determining how cancer treatments affect the risk of cardiovascular morbidities is essential, and the development of high-quality methods for collecting such data is critical. While self-reported data are adequate for assessing the presence of any CVD condition, medical record review will yield higher quality data on specific CVD conditions.