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
[{'content': 'Which of the following statements about Rheumatoid Factor is true - \nSelect and explain. \nA. It is an IgM antibody directed against IgG, B. It is an IgG antibody directed against IgM, C. It is more specific than Anti-CCP antibodies, D. It is positive in all cases of Juvenile Rheumatoid Arthritis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Rheumatoid factor in Rheumatoid Arthritis is an IgM antibody directed against the Fc fragment of IgG\nAnti CCP antibodies are most specific blood test for rheumatoid arthritis (specificity ∼ 95%).\nRheumatoid factor is positive in only 10% of patients with JRA.', 'role': 'assistant'}]