A 28-year-old woman with a history of recurrent jaundice and splenomegaly is investigated for hemolytic anemia. Laboratory findings show spherocytes on blood smear, positive direct antiglobulin test (DAT), elevated reticulocyte count, and elevated indirect bilirubin. All of the following are features of autoimmune hemolytic anemia (AIHA) EXCEPT:

Question

Accepted Answer

A. Spherocytes are the characteristic RBC morphology due to complement-mediated lysis. ## Distinguishing Autoimmune Hemolytic Anemia Variants

### Understanding the Correct Answer

**Key Point:** Spherocytes in AIHA result from **antibody-mediated opsonization and partial membrane loss**, NOT complement-mediated lysis. Complement-mediated lysis is the mechanism in cold agglutinin disease (CAD), not warm AIHA.

### Pathophysiology of RBC Destruction in AIHA

| Feature | Warm AIHA | Cold Agglutinin Disease |
|---------|-----------|------------------------|
| **Antibody type** | IgG (rarely IgM) | IgM (pentameric) |
| **Temperature optimum** | 37°C | 4°C |
| **RBC morphology** | Spherocytes (antibody coating) | Agglutination, then C3 complement |
| **Mechanism** | Opsonization → splenic macrophage removal → membrane loss | Complement activation → intravascular hemolysis |
| **DAT result** | IgG positive | C3 positive (IgM may wash off) |

**High-Yield:** Spherocytes form because IgG-coated RBCs are **partially phagocytosed** by splenic macrophages, losing membrane surface area. This is **NOT** complement-mediated lysis (which causes fragmentation and schistocytes, not spherocytes).

### Why Other Options Are Correct

1. **Warm AIHA is most common (60–70% of AIHA cases)** and typically responds to corticosteroids as first-line therapy — correct.
2. **Cold agglutinin disease** presents with acrocyanosis, Raynaud phenomenon, and hemoglobinuria in cold exposure — correct.
3. **Evans syndrome** = concurrent AIHA + immune thrombocytopenia (ITP) — correct.

### Clinical Pearl

**Complement-mediated hemolysis** (as in CAD) produces **intravascular hemolysis** with hemoglobinuria, elevated LDH, and low haptoglobin. **Antibody-mediated opsonization** (as in warm AIHA) produces **extravascular hemolysis** in the spleen with spherocytes and jaundice.

Answer

B. Warm AIHA is the most common form and responds well to corticosteroids

Answer

C. Cold agglutinin disease presents with acrocyanosis and Raynaud phenomenon in cold weather

Answer

D. Evans syndrome is the concurrent occurrence of AIHA and immune thrombocytopenia

Explanation

Distinguishing Autoimmune Hemolytic Anemia Variants

Understanding the Correct Answer

Pathophysiology of RBC Destruction in AIHA

Why Other Options Are Correct

Clinical Pearl

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Feature	Warm AIHA	Cold Agglutinin Disease
Antibody type	IgG (rarely IgM)	IgM (pentameric)
Temperature optimum	37°C	4°C
RBC morphology	Spherocytes (antibody coating)	Agglutination, then C3 complement
Mechanism	Opsonization → splenic macrophage removal → membrane loss	Complement activation → intravascular hemolysis
DAT result	IgG positive	C3 positive (IgM may wash off)