Autoimmune hemolytic anemia with an initially negative direct antiglobulin test: A diagnostic challenge

Abstract Background:Autoimmune hemolytic anemia (AIHA) is a clinical condition characterized by an autoimmune destruction of red blood cells (RBCs). Clinically, patients present with jaundice and scleral icterus and, in some cases, splenomegaly. Laboratory findings typically involve a predominant indirect hyperbilirubinemia, elevated lactate dehydrogenase (LDH) and low haptoglobin with an elevated reticulocyte index. AIHA can be further classified into warm and cold types based on the type of autoantibody involved. Cold AIHA is mediated by IgM antibodies and complement activation at lower temperatures, resulting in intravascular hemolysis. On the other hand, warm AIHA is driven by IgG antibodies binding to the surface of RBCs, resulting in an extravascular clearance by splenic macrophages. The diagnosis of AIHA hinges on the direct antiglobulin test (DAT), also known as the direct Coombs test, which detects bound antibodies or complements on the surface of RBCs. However, up to 5-10% of hospitalized patients with AIHA may initially test negative by DAT, complicating the diagnostic process (Barcellini & Fattizzo, 2020). Case: The patient is a41-year old man with history of Ehler Danlos Syndrome and no known history of hemolytic anemia or familial hereditary anemias who initially presented with jaundice, dark urine, and weakness days after completing a marathon. He was hemodynamically stable on arrival and found to have a hemoglobin of 10.3g/dL with MCV of 101fL with other laboratory findings consistent with hemolytic anemia: total bilirubin of 8.2mg/dL with an indirect hyperbilirubinemia of 7.8mg/dL, LDH of 794U/L, undetectable haptoglobin, and reticulocyte index of 3.3%. Renal function was preserved and creatinine kinase was found to be within normal limits. B12 and folate were within normal limits and iron panel revealed an elevated iron (268 µg/dL), high saturation (93%), and elevated ferritin (1560 ng/mL). Mild transaminitis prompted infectious evaluation and Lyme, Anaplasma/Ehrlichiosis, and Babesia studies were found to be negative. The initial DAT was negative, yet due to a strong clinical suspicion for AIHA, repeat DAT was obtained and revealed IgG antibodies, consistent with warm AIHA. The patient was subsequently started on corticosteroids and folate supplementation with clinical improvement. Conclusion: Although DAT remains the gold standard for diagnosing AIHA, clinicians should be aware of its potential for false negative results. In cases where clinical and laboratory findings strongly indicate an autoimmune component to the hemolytic anemia, repeat DAT testing and close monitoring are essential. This case highlights the diagnostic challenges and underscores the importance of maintaining a high index of suspicion for an AIHA despite an initial negative DAT.