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
RA is best diagnosed by? 
Select and explain. 
A. IgA RF\/, B. IgG RF\/, C. IgM RF\/, D. Anti CCP antibody
D: Anti CCP antibody
Answer: D: Anti CCP antibody 
Explanation: to establish diagnosis of rheumatoid ahritis are * Clinical criteria * ESR and CRP * Ultrasound or MRI * Rheumatoid factor and anti-citrullinated peptide antibodies DAVIDSON&;S 22nd EDITION;PAGE NO 1100