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: Pathology
A 23 years old female presented with jaundice and pallor for 2 months. Her peripheral blood smear shows the presence of spherocytes. The most relevant investigation to arrive at a diagnosis is - 
Select and explain. 
A. Retics count, B. Osmotic fragility test, C. Coombs test, D. Tests for PNH
C: Coombs test
Answer: C: Coombs test 
Explanation: . Coombs test