This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immune system, Subject name: Medicine
B cell functions is tested by all of the following except? 
Select and explain. 
A. C H 50 count, B. Amount of Ig G, C. PPD testing, D. Cytokine
A: C H 50 count
Answer: A: C H 50 count 
Explanation: measurement of CH 50 is the best screening test for defiency of classical and terminal pathways.hemolytic activity of compliment system is measured as the hemolysis of sheep erythrocytes sensitised by specific antibodies.the degree of hemolysis is measured by CH 50 REF:HARRISONS PRINCIPLE&;S OF INTERNAL MEDICINE 18TH EDITION