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Difficulty: MediumHematology and Oncology

A 35-year-old woman presents to the clinic reporting a two-week history of profound fatigue and breathlessness upon exertion. She also notes that her urine has appeared unusually dark over the past several days. The patient has no prior significant medical conditions and takes no daily medications. Her temperature is 37.2°C (99.0°F), blood pressure is 112/70 mmHg, pulse is 108/min, and respiratory rate is 18/min. Physical examination reveals noticeable yellowing of the sclerae, pale conjunctivae, and a palpable spleen tip 3 cm below the left costal margin. There is no abdominal tenderness.

Laboratory studies reveal the following:

TestResultReference Range
Hemoglobin7.6 g/dL12.0–15.5 g/dL
Mean corpuscular volume94 fL80–100 fL
Platelet count210,000/µL150,000–400,000/µL
Leukocyte count7,500/µL4,500–11,000/µL
Reticulocyte count8.2%0.5–1.5%
Total bilirubin3.8 mg/dL0.1–1.2 mg/dL
Direct bilirubin0.5 mg/dL0.0–0.3 mg/dL
Lactate dehydrogenase (LDH)680 U/L100–250 U/L
Haptoglobin< 10 mg/dL40–200 mg/dL

A peripheral blood smear demonstrates numerous dense, spherical red blood cells lacking central pallor.

Which of the following is the most appropriate next step in the evaluation of this patient's anemia?

  1. Direct antiglobulin testAnswer
  2. B
    Eosin-5-maleimide binding test
  3. C
    Right upper quadrant ultrasonography
  4. D
    Measurement of serum ferritin and iron levels
  5. E
    Flow cytometry for CD55 and CD59

Answer

The correct answer is the direct antiglobulin test (also known as the direct Coombs test).
This patient presents with classic clinical and laboratory signs of hemolytic anemia: fatigue, jaundice, indirect hyperbilirubinemia, elevated LDH, low haptoglobin, and a robust reticulocyte response. The peripheral blood smear reveals spherocytes, which are formed when splenic macrophages remove antibody-coated portions of the red blood cell membrane. The primary differential diagnosis for spherocytosis includes Autoimmune Hemolytic Anemia (AIHA) and Hereditary Spherocytosis (HS). The direct antiglobulin test (DAT) is the essential next step to distinguish between the two; a positive result indicates immune-mediated destruction (AIHA), which is highly likely in an adult patient with acute symptom onset and no chronic family history of anemia.

Step-by-Step Solution

1
Interpret the clinical presentation and laboratory results.
The patient has normocytic anemia, robust reticulocytosis, unconjugated (indirect) hyperbilirubinemia, elevated LDH, and low haptoglobin.
These combined findings definitively confirm the presence of an active hemolytic process.
2
Analyze the peripheral blood smear findings.
Spherocytes (dense, spherical red blood cells lacking central pallor) are present.
Spherocytes are characteristically seen in two main conditions: immune-mediated destruction of red blood cell membranes (Autoimmune Hemolytic Anemia) and congenital cytoskeletal defects (Hereditary Spherocytosis).
3
Determine the most appropriate diagnostic test to differentiate the causes of spherocytosis.
The direct antiglobulin test (DAT) should be ordered.
In a 35-year-old adult presenting with an acute onset of symptoms and no prior family history, acquired Autoimmune Hemolytic Anemia is the most likely diagnosis. The DAT will identify IgG antibodies and/or complement bound to the red blood cell surface, confirming the immune etiology.

Key Concept

The evaluation of hemolytic anemia presenting with spherocytes requires a direct antiglobulin (Coombs) test to differentiate autoimmune hemolytic anemia (AIHA) from hereditary spherocytosis (HS).
Estimated Time:1m 30s
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Topics

Hematology and Oncology

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