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
A 23 year old female presenting with anemia, jaundice, for 2 years, peripheral smear showing spherocytes, the best investigation to be done - 
Select and explain. 
A. Reticulocyte count, B. Osmotic fragility test, C. Coombs test, D. Bone marrow aspiration
C: Coombs test
Answer: C: Coombs test 
Explanation: None