What is the investigation of choice for a white girl with chronic anaemia, enlarged spleen, increased reticulocyte count and reduced haptoglobin levels?

The scenario describes a young girl exhibiting symptoms that suggest a hemolytic process due to chronic anemia, an enlarged spleen (splenomegaly), an increased reticulocyte count indicating the bone marrow is responding to anemia by producing more red blood cells, and reduced haptoglobin levels, which are often low in cases of hemolysis.

In this context, the osmotic fragility test is used to evaluate the integrity of red blood cells. Increased fragility indicates that the red blood cells are more susceptible to hemolysis in hypotonic solutions, which is characteristic of certain conditions like hereditary spherocytosis. Given the symptoms provided, this test would help determine whether hereditary spherocytosis or another type of hemolytic anemia is present.

Other options would not provide as direct information regarding the cause of the chronic anemia and splenomegaly. For instance, while a blood transfusion could address the anemia, it does not investigate the underlying cause. A bone marrow biopsy assesses the production of blood cells but does not directly evaluate hemolytic conditions. A direct Coombs test identifies autoimmune hemolytic processes but would not specifically address membrane integrity issues. Thus, the osmotic fragility test is specifically designed to investigate