A 6-year-old boy of African descent presents with acute chest pain, fever, and shortness of breath. Clinical examination reveals hepatosplenomegaly and bone tenderness. A peripheral blood smear shows sickle-shaped RBCs. Which investigation is most appropriate to confirm the diagnosis of sickle cell disease?

Explanation

## Diagnostic Confirmation in Sickle Cell Disease ### Why HPLC is the Gold Standard **High-Yield:** HPLC (High-Performance Liquid Chromatography) is the gold standard and most specific test for confirming sickle cell disease. It definitively identifies and quantifies hemoglobin variants (HbS, HbA, HbF, HbA2) and can distinguish between sickle cell disease (HbSS), sickle cell trait (HbAS), and other hemoglobinopathies. ### Diagnostic Algorithm for SCD ```mermaid flowchart TD A[Clinical suspicion of SCD]:::outcome --> B[Peripheral smear + CBC]:::action B --> C{Sickle cells seen?}:::decision C -->|Yes| D[Hemoglobin electrophoresis/HPLC]:::action D --> E[Confirms HbS pattern]:::outcome C -->|No| F[Rule out other hemolysis]:::action E --> G{HbSS vs HbAS vs HbC-S?}:::decision G -->|HbSS| H[Sickle Cell Disease]:::outcome G -->|HbAS| I[Sickle Cell Trait]:::outcome ``` ### Comparison of Investigations | Investigation | Principle | Specificity | Use in SCD | | --- | --- | --- | --- | | **HPLC** | Separates Hb variants by charge & hydrophobicity | Very high (>99%) | Gold standard for diagnosis & typing | | **Hemoglobin electrophoresis** | Separates Hb by electrical charge | High | Confirmatory; less precise than HPLC | | **Sickle solubility test** | Hb polymerization in reducing conditions | Moderate | Screening test; positive in HbS trait & disease | | **Osmotic fragility** | RBC membrane integrity | Low | Not specific for SCD; used in hereditary spherocytosis | | **Reticulocyte count** | Immature RBC percentage | Low | Indicates hemolysis severity, not diagnostic | **Key Point:** While a sickle solubility test (dithionite) is a rapid screening tool, it cannot distinguish between sickle cell disease and sickle cell trait. HPLC provides both diagnosis AND phenotyping in a single test. **Clinical Pearl:** In India, HPLC or cellulose acetate electrophoresis at pH 8.6 is recommended by the Indian Academy of Pediatrics for all suspected cases of hemoglobinopathy.