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Difficulty: MediumHematology and Oncology

A 2828-year-old woman presents to the clinic complaining of worsening fatigue, exertional dyspnea, and yellowing of her eyes over the past two weeks. Her past medical history is significant for systemic lupus erythematosus (SLE), which has been well-controlled on hydroxychloroquine. Vital signs are within normal limits except for a heart rate of 112112/min. Physical examination reveals scleral icterus and pale conjunctivae. The spleen is palpable 33 cm below the left costal margin. Laboratory studies reveal the following:

TestResult
Hemoglobin7.27.2 g/dL
Mean corpuscular volume105105 fL
Platelets210,000210,000/mm3^3
Leukocytes5,4005,400/mm3^3
Reticulocyte count12%12\%
Total bilirubin4.14.1 mg/dL
Direct bilirubin0.60.6 mg/dL
Lactate dehydrogenase650650 U/L
Haptoglobin<10<10 mg/dL

A peripheral blood smear demonstrates normochromic red blood cells, marked polychromasia, and numerous spherocytes. No schistocytes are seen. Which of the following is the most appropriate next step to establish the diagnosis?

  1. Direct antiglobulin testAnswer
  2. B
    Osmotic fragility test
  3. C
    Flow cytometry for CD55 and CD59
  4. D
    ADAMTS13 activity level
  5. E
    Hemoglobin electrophoresis

Answer

Direct antiglobulin test
The correct answer is the direct antiglobulin test. This patient presents with classic signs of hemolytic anemia: elevated reticulocytes (leading to a high MCV due to their larger size), indirect hyperbilirubinemia, elevated LDH, and decreased haptoglobin. The peripheral smear reveals spherocytes, which are formed when splenic macrophages consume portions of antibody-coated red blood cell membranes. In a young woman with a history of systemic lupus erythematosus (SLE), the acute onset of spherocytic hemolytic anemia is highly suspicious for Warm Autoimmune Hemolytic Anemia (AIHA). The definitive next step in diagnosis is the direct antiglobulin test (DAT, or direct Coombs test), which identifies the presence of IgG or C3 bound to the red blood cell surface.

Step-by-Step Solution

1
Analyze the laboratory data to identify the presence and type of anemia.
The patient has a macrocytic anemia with an elevated reticulocyte count, indirect hyperbilirubinemia, elevated LDH, and low haptoglobin, which points definitively to a hemolytic process.
Establishing the mechanism of anemia is the first step in narrowing the differential diagnosis.
2
Correlate the peripheral smear findings with the patient's medical history.
The smear shows spherocytes. Given her established history of systemic lupus erythematosus (SLE) and acute symptom onset, this suggests an acquired autoimmune process rather than a congenital defect.
Spherocytes can be seen in both hereditary spherocytosis and autoimmune hemolytic anemia; clinical context distinguishes the two.
3
Determine the definitive diagnostic test for the suspected condition.
The most appropriate test to confirm Warm Autoimmune Hemolytic Anemia (AIHA) is the direct antiglobulin (Coombs) test.
This test detects IgG antibodies and/or C3 complement bound directly to the red blood cell surface, confirming the autoimmune etiology.

Key Concept

Diagnosis of Autoimmune Hemolytic Anemia in patients with underlying autoimmune disease
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Topics

Hematology and Oncology

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