This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
The gold standard test to diagnose PNH is: 
Select and explain. 
A. Bone marrow study, B. Sucrose hemolysis test, C. Flow cytometry, D. Genetic study
C: Flow cytometry
Answer: C: Flow cytometry 
Explanation: The gold standard test to diagnose PNH today is flow cytometry. Reference: Harrisons Principles of Internal Medicine, 18th Edition, Page 884