The graph below depicts the results of a red cell osmotic fragility test. The dashed curve represents which of the following?
Drug-induced hemolytic anemia
Glucose-6-phosphate dehydrogenase deficiency
Ans : B Hereditary spherocytosis
It is an autosomal dominant disorder, is characterized by an abnormality of the skeleton of the red cell membrane that makes the erythrocyte spherical, less deformable, and vulnerable to splenic sequestration and destruction (extravascular hemolysis).
This mild to moderate hemolytic anemia can lead to splenomegaly, jaundice, and pigmented gallstones.
In HS, the defect in the spectrin molecule results in decreased binding to protein 4.1.
This decreases the amount of red blood cell membrane and causes the formation of spherocytes (because of the low surface-to volume ratio).
Spherocytes in a peripheral blood smear show a smaller diameter than normal and an apparent increase in hemoglobin concentration because of a decrease in cell surface, with consequent deeper staining for hemoglobin.
The increase in hemoglobin concentration within the red cells can be seen clinically as an increase in the mean cell hemoglobin concentration (MCHC).
The osmotic fragility test can be used to document the presence of spherocytes in the peripheral blood.
Spherocytes lyse at a higher concentration of sodium chloride than do normal red cells.
In contrast, flat hypochromic cells, such as those in thalassemia, have a greater capacity to expand in dilute salt solution and thus lyse at a lower concentration.
The longer the incubation of the red cells in these salt concentrations, the greater the response to osmotic autoimmune hemolytic anemia.