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
Which of the following statements about Rheumatoid Factor is true - 
Select and explain. 
A. 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
A: It is an IgM antibody directed against IgG
Answer: A: It is an IgM antibody directed against IgG 
Explanation: Rheumatoid factor in Rheumatoid Arthritis is an IgM antibody directed against the Fc fragment of IgG
Anti CCP antibodies are most specific blood test for rheumatoid arthritis (specificity ∼ 95%).
Rheumatoid factor is positive in only 10% of patients with JRA.