Blood donors with positive direct antiglobulin tests are at increased risk for cancer

Background: Positive direct antiglobulin tests (DATs) have been associated with both autoimmunity and lymphoproliferative disorders. However, it is unknown whether DAT+ in healthy blood donors is associated with an increased risk of malignancies. Study Design and Methods: In the current study, all blood donors with DAT+ samples were identified during the years 1999 through 2003 through the Magen David Adom National Blood Services in Israel. This study compared the risk of cancer among 586 DAT+ and 2344 DAT- donors who were matched according to sex, age, and year of donation. The risk of cancer in DAT+ donors was also compared to expected rates in the general Israeli population. Cancer was ascertained through the Israel Cancer Registry. Results: Malignancies occurred among 17 (2.9%) of the DAT+ and 27 (1.2%) of the DAT- blood donors; of these, 3 donors in the DAT+ group were diagnosed with hematopoietic malignancies within 12 months of their donation. Even after excluding these early cases, the relative risk of developing cancer was 2.14 (95% confidence interval [CI], 1.13-4.10) comparing DAT+ with DAT- donors, while the relative risk for hematopoietic cancer was 8.3 (95% CI, 1.5-43.2). Comparing DAT+ blood donors with the general population, the standardized incidence ratios (observed/expected cases) were elevated at 2.11 (95% CI, 1.15-3.54; p = 0.16) for all malignancies and 8.03 (95% CI, 2.2-20.6; p = 0.003) for hematologic malignancies. Conclusion: There is evidence of a significantly increased risk of cancer, especially hematologic malignancies, among blood donors with a positive DAT even within a short follow-up period.