Unstable Hemoglobin Variants: Molecular Mechanisms, Clinical Phenotypes, and a Practical Diagnostic and Management Approach

Unstable hemoglobin variants are rare structural hemoglobin disorders in which alterations in the globin chain reduce hemoglobin stability, promoting denaturation, precipitation, and red cell injury. Affected individuals may present with a broad spectrum, ranging from compensated hemolysis to severe transfusion-dependent anemia, and episodes are commonly exacerbated by intercurrent illness or oxidative stress. Diagnosis remains challenging because many unstable variants are not readily recognized by routine hemoglobin separation, and classic morphological clues (Heinz bodies; bite/blister cells) are neither uniformly present nor specific. This review summarizes the molecular mechanisms underlying hemoglobin instability, outlines phenotypic patterns across the lifespan (including neonatal-limited instability involving fetal hemoglobin), and provides a practical diagnostic framework that integrates hemoglobin separation methods, stability assays, and molecular testing. Supportive care, including avoidance of oxidant triggers, folate supplementation, and transfusion support when needed, remains the mainstay, while splenectomy and curative transplantation are reserved for selected severe cases.