Most specific antibody seen in RA -

Ans. is 'a' i.e., Anti CCP Laboratory features of Rheumatoid Arthritis:* IgM, IgG, and IgA isotypes of RF occur in sera from patients with RA, although the IgM isotype is the one most frequently measured by commercial laboratories.* Serum IgM RF has been found in 75-80% of patients with RA; therefore, a negative result does not exclude the presence of this disease.* It is also found in other connectivetissue diseases, such as primary Sjogren's syndrome, systemic lupus erythematosus, and type II mixed essential cryoglobulinemia,as well as chronic infections such as subacute bacterial endocarditis and hepatitis B and C.* Serum RF may also be detected in 1-5% ofthe healthy population.* The presence of serum anti-CCP antibodies has about the same sensitivity as serum RF for the diagnosis of RA.* However, its diagnostic specificity approaches 95% (most specific for RA), so a positive test for anti- CCPantibodies in the setting of an early inflammatory arthritis is usefulfor distinguishing RA from other forms of arthritis.* There is some incremental value in testing for the presence of both RF and anti-CCP, as some patients with RA are positive for RF but negative foranti-CCP and visa versa.* The presence of RF or anti-CCP antibodies also has prognostic significance, with anti-CCP antibodies showing the most value for predicting worse outcomes.