This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thalassemia, Subject name: Medicine
A 30-year-old female, RBC count 4.5 million, MCV- 55 fl, TLC- 7000, no history of blood transfusion, Mentzer index - 12. Diagnosis is? 
Select and explain. 
A. Iron deficiency anemia, B. Thalassemia major, C. Thalassemia minor, D. Megaloblastic anemia
C: Thalassemia minor
Answer: C: Thalassemia minor 
Explanation: * Since MCV is reduced this indicates microcytic anemia, which rules out choice D. * No history of blood transfusion rules out thalassemia major. * Mentzer index = MCV/RBC count If mentzer index < 13 - Thalassemia minor > 13 - Iron deficiency The Mentzer index in the given question is - 12 thus it is most likely a case of thalassemia minor.