156 - How to follow-up the patient with unexpected autoantibody positivity

“Unexpected” positivities of autoantibody assays are not infrequent, and will probably increase with the increasing use of microarray systems able to simultaneously evaluate a great number of autoantibody specificities. The problems raised by some relatively common “unexpected” positivities (antinuclear, antithyroid, antiphospholipid and antitissue transglutaminase autoantibodies) are discussed in this article. The follow up of subjects with such unexpected findings should be planned taking into account that autoantibody positivities are far more frequent than autoimmune diseases, although autoantibodies may be risk factors for clinical autoimmune disease or also may play a pathogenetical role. The positive predictive value of an autoantibody positivity depends upon the diagnostic accuracy of the test used and disease prevalence. Unexpected nuclear autoantibody positivities have a low positive predictive value for systemic autoimmune disease. Phospholipid autoantibodies deserve more attention due to their possible pathogenic role, as well as tissue transglutaminase autoantibodies due to their very high positive predictive value for celiac disease. This review aims to discuss the specific strategies that should be adopted when an unexpected antibody positivity is found