Which laboratory finding best distinguishes G6PD deficiency from autoimmune hemolytic anemia (AIHA)?

Explanation

## Distinguishing G6PD Deficiency from Autoimmune Hemolytic Anemia ### Pathophysiology and Laboratory Differentiation | Feature | G6PD Deficiency | Autoimmune Hemolytic Anemia (AIHA) | |---------|-----------------|------------------------------------| | **Mechanism** | Oxidative stress → RBC denaturation | IgG/IgM antibodies against RBC antigens | | **DAT/Coombs Test** | **Negative** | **Positive** | | **Heinz Bodies** | **Present** (on supravital staining) | Absent | | **Spherocytes** | Absent | Present | | **Hemolysis Trigger** | Oxidative stress (drugs, infection, fava beans) | Spontaneous or secondary | | **Hemoglobin Pattern** | Normal | Normal | | **RBC Morphology** | Bite cells, blister cells | Spherocytes, polychromasia | | **Inheritance** | X-linked recessive | Acquired (autoimmune) | | **Haptoglobin** | Decreased | Decreased | **Key Point:** **Heinz bodies on supravital staining** are the pathognomonic finding in G6PD deficiency. These are denatured hemoglobin precipitates (Heinz-Koehler bodies) that form when oxidative stress overwhelms the RBC's antioxidant defense. They are **absent in AIHA**, where the primary mechanism is antibody-mediated RBC destruction. **High-Yield:** The **DAT/Coombs test is the gold standard discriminator** between these two conditions: - **G6PD deficiency: DAT NEGATIVE** (no antibodies on RBC surface) - **AIHA: DAT POSITIVE** (IgG and/or IgM coating RBCs) However, since the question asks for the **best discriminating feature** among the options, **Heinz bodies** are the most specific morphologic finding unique to G6PD. **Mnemonic:** **"HEINZ = Hemoglobin Enzyme deficiency (G6PD)"** — Heinz bodies are pathognomonic for G6PD deficiency. **Clinical Pearl:** Bite cells (RBCs with a "bite" taken out, representing Heinz body removal by the spleen) are also characteristic of G6PD deficiency and are **never seen in AIHA**. Spherocytes, conversely, are the hallmark of AIHA and are absent in G6PD deficiency unless there is concurrent hereditary spherocytosis. **Tip:** When you see **Heinz bodies on supravital staining**, immediately think **G6PD deficiency**. When you see **positive DAT + spherocytes**, think **AIHA**. [cite:Robbins 10e Ch 13]