This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hemolytic Anemias: Basic concepts and classification, Subject name: Pathology
A 39-year-old man repos seeing red-colored urine in the morning. The CBC reveals anemia, low serum iron, and an elevated reticulocyte count. Laboratory studies show increased lysis of erythrocytes when incubated with either sucrose or acidified serum. Which of the following is the appropriate diagnosis 
Select and explain. 
A. Anemia of chronic renal failure, B. Hereditary spherocytosis, C. Microangiopathic hemolytic anemia, D. Paroxysmal nocturnal hemoglobinuria
D: Paroxysmal nocturnal hemoglobinuria
Answer: D: Paroxysmal nocturnal hemoglobinuria 
Explanation: - Given clinical features suggests the diagnosis of PNH - Despite its name, the disorder is nocturnal in only a minority of cases. - PNH is a clonal stem cell disorder characterized by episodic intravascular hemolytic anemia; secondary to increased sensitivity of erythrocytes to complement-mediated lysis. - It is d/t somatic mutation of phosphatidylinositol glycan-class A (PIG-A) gene. - Most useful diagnostic test is flow cytofluorometry. - other tests used are: Sucrose hemolysis test Acidified serum (Ham test) - Choices B and C are hemolytic conditions, do not show increased lysis in described laboratory studies.