Department of Laboratory Medicine and Pathology, University of Washington, Washington, United States
Background/Case Studies: The workup of immune-mediated hemolytic anemia includes a direct antiglobulin test (DAT) to investigate the presence of IgG or complement to evaluate for the presence of auto or alloantibodies. A standard DAT can be performed by many blood banks onsite and aids in clinical diagnosis and treatment of hemolytic anemia. However, in cases with a strong clinical suspicion for immune-mediated hemolysis, clinicians will send out an enhanced DAT, also known as “Super Coombs”, to an immunohematology reference laboratory (IRL). This test evaluates for low-affinity or low concentration IgG, complement, IgM, and IgA coating red blood cells. The impact of these test results on clinical management is unclear. The purpose of this study was to conduct a retrospective review of the yield of enhanced DAT compared to in-house standard DAT and its impact on clinical management.
Study
Design/Methods: All enhanced DAT testing sent out from the University of Washington to multiple IRLs from January 2017 to January 2024 were identified. Associated metadata, including corresponding in-house DAT results, collection dates, medical record numbers, and ordering providers were collected. Lastly, a retrospective chart review of each patient was conducted to determine patient outcomes.
Results/Findings: A total of 22 tests were sent out (female=13, male=9), and among these, two results were not found. Of these, a majority of the tests (n=18/20, 90%) were negative by in-house standard DAT and only 10% of the resulted tests (n=2/20) had concurrent positivity with in-house standard DAT. 50% of tests (n=10/20) were found to be positive by enhanced DAT. Of these, six were C3 positive and five were low-affinity IgG positive (figure A). For the 10 positive results, four did not change management either because the results were interpreted as negative due to weak reactions (n=2), in-house DAT was already positive (n=1), or the results were lost to follow-up (n=1). For the six where management changed, four were due to presence of weak binding to complement on standard DAT methods leading to diagnosis of cold agglutinin disease (CAD), and two were due to low affinity IgG supporting a diagnosis of autoimmune hemolytic anemia. In one of the CAD cases, our in-house DAT was already positive, consistent with cold autoantibody. Overall, only 5 of 22 (22%) of the enhanced DAT ordered resulted in changes in clinical management. Conclusions: The findings are consistent with the existing literature that show around 40-50% DAT positivity upon enhanced testing with the greatest discrepancy with anti-C3. This study demonstrates that even positive enhanced DAT results may still be interpreted as negative and do not change clinical management. Further studies are needed to improve laboratory stewardship on the use of enhanced DATs.
