A 71-year-old man with a 4-year history of chronic lymphocytic leukemia (CLL) presents to the emergency department with progressive fatigue and exertional dyspnea over the past week. He has not required treatment for his CLL and has been managed with observation. On physical examination, he appears pale, has mild scleral icterus, and is tachycardic. There is no new lymphadenopathy, but his baseline splenomegaly is unchanged.
Laboratory studies show the following:
Hemoglobin: 7.2 g/dL (Baseline: 13.2 g/dL)
Mean corpuscular volume (MCV): 104 fL
Reticulocyte count: 8% (elevated)
Total bilirubin: 2.8 mg/dL
Indirect bilirubin: 2.1 mg/dL
Lactate dehydrogenase (LDH): 550 U/L (elevated)
Haptoglobin: Undetectable
Which of the following is the most likely finding on further diagnostic testing?
The correct answer is:
C) Positive direct antiglobulin (Coombs) test for IgG
This patient is experiencing warm autoimmune hemolytic anemia (W-AIHA), a well-recognized complication of CLL. AIHA occurs in approximately 5–10% of CLL patients. It is caused by the production of polyclonal IgG autoantibodies, usually by the remaining non-malignant B-cells, directed against Rh antigens on the red blood cell surface.
The clinical and laboratory features of AIHA include:
Evidence of hemolysis: Low haptoglobin, elevated indirect bilirubin, and elevated LDH.
Regenerative response: Elevated reticulocyte count (unless there is concurrent bone marrow suppression).
Spherocytes: On peripheral smear, small, dense red cells without central pallor are often seen because splenic macrophages partially nibble the IgG-coated membrane.
The direct antiglobulin test (DAT), or direct Coombs test, is the gold standard for diagnosis. In W-AIHA, the test is typically positive for IgG, with or without C3.
Answer choice B: Positive for C3 only, is incorrect. This finding is characteristic of cold agglutinin disease (CAD), which is mediated by IgM antibodies. While CAD can occur in lymphoid malignancies, W-AIHA (IgG) is significantly more common in CLL.
Answer choice E: Reduced ADAMTS13, is incorrect. This is the mechanism for thrombotic thrombocytopenic purpura (TTP). While TTP causes microangiopathic hemolytic anemia (MAHA), it would present with schistocytes on the smear and a negative Coombs test.
Answer choice D: Presence of bite cells and Heinz bodies on peripheral smear, is incorrect. These are the hallmarks of G6PD deficiency. Hemolysis in G6PD is usually triggered by oxidative stress (e.g., fava beans, infections, or sulfa drugs) and is Coombs negative.
Answer choice A: Flow cytometry showing absence of CD55 and CD59 on red cells, is incorrect. This is the diagnostic finding for paroxysmal nocturnal hemoglobinuria (PNH), an acquired stem cell defect. PNH presents with intravascular hemolysis and nocturnal hematuria but is not specifically associated with CLL.
Key Learning Point
Warm autoimmune hemolytic anemia (AIHA) is a common secondary complication of CLL. It presents as a sudden drop in hemoglobin with markers of extravascular hemolysis (spherocytes, high LDH, low haptoglobin). The diagnosis is confirmed by a positive direct Coombs (DAT) for IgG. First-line treatment typically involves corticosteroids (e.g., prednisone), even if the underlying CLL does not yet require treatment.
