Decreased osmotic fragility is not seen in which of the following conditions?
**Core Concept**
Decreased osmotic fragility refers to the reduced susceptibility of red blood cells (RBCs) to hemolysis when exposed to hypotonic solutions. This phenomenon can occur due to various alterations in the RBC membrane, affecting its osmotic stability.
**Why the Correct Answer is Right**
The osmotic fragility of RBCs is influenced by the amount of hemoglobin and the flexibility of the cell membrane. Conditions that affect these factors can alter the osmotic fragility. Thalassemia major, also known as beta-thalassemia, is a genetic disorder characterized by a significant reduction in the production of the beta-globin chains of hemoglobin. This leads to a decrease in the amount of hemoglobin in RBCs, making them more resistant to hemolysis in hypotonic solutions.
**Why Each Wrong Option is Incorrect**
**Option A:** Hereditary spherocytosis - This condition is characterized by a mutation in the genes encoding proteins of the RBC membrane skeleton, leading to decreased osmotic fragility due to the spherocytic shape of the RBCs, not increased.
**Option B:** G6PD deficiency - This is an enzyme deficiency that makes RBCs more susceptible to hemolysis in response to oxidative stress, not decreased osmotic fragility.
**Option C:** Sickle cell disease - This condition is characterized by a mutation in the HBB gene, leading to abnormal hemoglobin (HbS) that polymerizes under low oxygen conditions, causing RBCs to become sickle-shaped and leading to decreased osmotic fragility.
**Clinical Pearl / High-Yield Fact**
The osmotic fragility of RBCs can be affected by various conditions, including genetic disorders, enzymatic deficiencies, and membrane abnormalities. Understanding these factors is crucial for diagnosing and managing patients with hemolytic disorders.
**Correct Answer: D. Thalassemia major**