Understanding antinuclear antibodies.

The American College of Rheumatology (formerly the American Rheumatism Association) diagnostic criteria for connective tissue disorders frequently include positive antinuclear antibody (ANA) assays. Proper interpretation of these tests requires an understanding of the principles governing ANA assays. Assay results are reported in two ways: as titers and as descriptions of fluorescent patterns. A titer is a quantitative measure of ANAs in serum. Different patterns of immunofluorescence are associated with different subsets of collagen vascular disease. Positive results can occur in the absence of connective tissue disease. Accurate diagnosis of connective tissue disorders requires judicious use of ANA assays as well as skillful interpretation of the results.