Dissecting the direct antiglobulin test in warm autoimmune hemolytic anemia: clinical and laboratory correlations

OBJECTIVES: The direct antiglobulin test (DAT) is critical in determining whether a patient has an immune-mediated hemolytic process, but the appropriate interpretation of this test requires a nuanced understanding of what it measures, how it is performed, and how it is reported by the clinical laboratory. METHODS: To avoid diagnostic errors, the DAT must not be viewed in isolation. Instead, it should be assessed in combination with other blood bank testing, hemolytic laboratory testing, and patients' clinical condition. In this way, accurate diagnosis of an immune-mediated hemolytic process can ensue, including the diagnosis of warm autoimmune hemolytic anemia. RESULTS: This review sheds light on 2 scenarios that require an enhanced understanding of the DAT: (1) the DAT as a marker for warm autoimmune hemolytic anemia and (2) the DAT in cases of so-called "Coombs'-negative" or DAT-negative hemolytic anemia. CONCLUSIONS: A more comprehensive view of the DAT, including its diagnostic strengths and weaknesses, will reduce the risk of overcalling autoimmune hemolysis in patients with positive DATs and undercalling autoimmune hemolysis in patients with negative testing.