Why should an RF not be ordered in the evaluation of patients with acute polyarticular symptoms?
RF has a low sensitivity and specificity for RA in patients with acute polyarticular symptoms. Serum RF may be positive in acute infectious syndromes caused by hepatitis B, Epstein–Barr, influenza, and other viruses, but disappears as the viral syndrome resolves. In addition, while the sensitivity of RF approaches 75% to 85% among patients with established RA, it may be found in only 50% to 70% of patients upon initial evaluation
