American Board of Internal Medicine (ABIM) Certification Practice Exam

Which method is utilized to diagnose paroxysmal nocturnal hemoglobinuria (PNH)?

1. Bone marrow biopsy

2. Flow cytometry

3. Serum electrophoresis

4. Complete blood count

The correct answer is: Flow cytometry

The method used to diagnose paroxysmal nocturnal hemoglobinuria (PNH) is flow cytometry. PNH is a rare blood disorder caused by a mutation in the PIGA gene, leading to defective anchoring of certain proteins on the surface of red blood cells. These proteins are important for protecting the red blood cells from destruction by the immune system. Flow cytometry allows for the identification of these abnormal cells by analyzing the surface markers on the erythrocytes. Specifically, it detects the absence of GPI-anchored proteins, which are commonly present on normal blood cells. In PNH, the absence of these proteins indicates the presence of PNH clones within the population of red blood cells. Other methods, such as a bone marrow biopsy, serum electrophoresis, and complete blood count, do not provide the necessary information regarding the specific changes in red blood cell populations or the presence of the PNH clone. While a complete blood count may show signs of hemolysis or bone marrow failure, it cannot definitively diagnose PNH. Bone marrow biopsies can be beneficial for other hematological disorders and may show hypercellularity or other changes but are not specific for PNH. Serum electrophoresis is primarily used to evaluate