<prompt> Which of the following best represents the impoance of Rheumatoid factor in rheumatoid ahritis?Rheumatoid factor is associated with bad prognosisRheumatoid factor correlates with disease activityRheumatoid factor is very common in childhood Rheumatoid ahritisAbsent rheumatoid factor rules out the diagnosis of Rheumatoid ahritis  <response>: Rheumatoid factor RF consists of heterogeneous autoantibodies of the IgM class that react against the Fc region of human IgG. It is found in 70 of rheumatoid ahritis patients and is associated with a worse prognosis, since higher levels of rheumatoid factor are associated with more aggressive disease, rheumatoid nodules and extra aicular manifestations. Ref: Elective Hand Surgery: Rheumatological and Degenerative Conditions, Nerve Compression Syndromes By Michel Merle, Page 97 ; Measuring Immunity: Basic biology and Clinical Assessment By Michael T. Lotz, Page 189 