Certified Pediatric Hematology Oncology Nurse (CPHON) Practice Exam

The osmotic fragility test is specifically used to diagnose hereditary spherocytosis by assessing the stability of red blood cells when exposed to varying concentrations of saline. In this condition, red blood cells are abnormally spherical and less flexible, making them more susceptible to hemolysis (destruction) when placed in hypotonic solutions. During the test, if the red blood cells from a patient with hereditary spherocytosis are exposed to diluted saline, they will lyse more easily compared to normal cells. This increased sensitivity provides strong evidence for the diagnosis of hereditary spherocytosis.

In contrast, a CT scan and ultrasound are imaging studies that do not directly assess red blood cell morphology or fragility and are not used to identify this specific hematologic condition. A bone marrow biopsy is primarily used to evaluate bone marrow function and to investigate various blood disorders but does not confirm hereditary spherocytosis since the condition is related to the structure and stability of red blood cells rather than bone marrow pathology.