A 38-year-old woman from rural Maharashtra presents with a 3-month history of progressive fatigue, dyspnea on exertion, and jaundice. On examination, she is pale with mild hepatosplenomegaly. Laboratory investigations reveal hemoglobin 7.2 g/dL, reticulocyte count 8%, indirect bilirubin 3.2 mg/dL, and LDH 680 U/L. Peripheral blood smear shows numerous spherocytes, polychromasia, and occasional microspherocytes. Direct antiglobulin test (DAT/Coombs) is positive. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Autoimmune Hemolytic Anemia (AIHA) ### Key Diagnostic Features **Key Point:** The positive direct antiglobulin test (DAT/Coombs) is the gold standard confirmatory test for AIHA and distinguishes it from other hemolytic anemias with similar morphology. ### Peripheral Blood Smear Findings in AIHA | Finding | Significance | |---------|-------------| | **Spherocytes** | RBCs coated with IgG antibodies; loss of biconcave shape due to membrane loss | | **Polychromasia** | Reticulocytosis (8% here) indicating bone marrow response | | **Microspherocytes** | Smaller, denser spheres from repeated antibody-mediated membrane loss | | **Agglutination** | May be seen if cold agglutinins present (warm AIHA typically does not agglutinate) | ### Laboratory Findings Supporting AIHA 1. **Positive DAT (Coombs test)** — detects IgG/IgM/complement on RBC surface 2. **Elevated reticulocyte count** (8%) — appropriate marrow response 3. **Elevated indirect bilirubin** (3.2 mg/dL) — from RBC hemolysis 4. **Elevated LDH** (680 U/L) — released from lysed RBCs 5. **Low haptoglobin** — consumed by free hemoglobin binding **High-Yield:** Warm AIHA (IgG-mediated) is the most common form (~70% of AIHA cases) and presents with insidious onset, fatigue, and jaundice—exactly this patient's presentation. ### Pathophysiology ```mermaid flowchart TD A[Autoimmune trigger<br/>SLE, drugs, idiopathic]:::outcome --> B[IgG antibody production<br/>against RBC antigens]:::outcome B --> C[RBC opsonization<br/>with IgG]:::outcome C --> D[Splenic macrophage<br/>recognition]:::action D --> E[Partial or complete<br/>RBC phagocytosis]:::action E --> F[Spherocyte formation<br/>from membrane loss]:::outcome F --> G[Positive DAT test]:::outcome G --> H[Hemolytic anemia<br/>with reticulocytosis]:::outcome ``` **Clinical Pearl:** The combination of **positive DAT + spherocytes + polychromasia + elevated indirect bilirubin** is pathognomonic for AIHA. DAT positivity is the distinguishing feature that rules out hereditary spherocytosis. ### Why This Patient Has AIHA, Not Hereditary Spherocytosis - **DAT is positive** — hereditary spherocytosis DAT is always negative - **Acute presentation** (3 months) — hereditary spherocytosis is lifelong, often diagnosed in childhood - **No family history mentioned** — hereditary spherocytosis is autosomal dominant - **Jaundice and hepatosplenomegaly** — more typical of acquired hemolysis **Mnemonic: AIHA Features = "DISH"** - **D**AT positive (Direct Antiglobulin Test) - **I**ncreased indirect bilirubin - **S**phericytes on smear - **H**emolytic anemia (elevated reticulocytes, LDH) [cite:Robbins 10e Ch 13]