What will be the most appropriate investigation for a 40 year female presenting with anemia, jaundice and spherocytosis?

Presence of anaemia, jaundice and spherocytosis in a 40 yr old female patient is consistent with the diagnosis of both hereditary spherocytosis and auto immune hemolytic anemia. Hereditary spherocytosis must be distinguished primarily from the spherocytic hemolytic anemia associated with RBC antibodies. Coomb's test is the next best investigation of choice to differentiate between the two. Positive Coomb's test indicates auto immune hemolytic anaemia. So Coomb's test is the single best answer of choice. Ref: Harrison's Principles of Internal Medicine, 16th Edition, Pages 607-9; Manual of Practical Medicine By R Alagappan, 3rd Edition, Pages 331-2