Circulating autoantibodies are diagnostic markers for a variety of autoimmune diseases including rheumatoid arthritis, scleroderma, Sjögren's syndrome, systemic lupus erythematosus, and autoimmune hepatitis. Since only view studies exist on individuals without known diseases, we analyzed the prevalence of frequently determined autoantibodies in "healthy" individuals.

111 individuals (43 female, 68 male; mean age 58 +/- 13 years, median 58, range 22-89), in whom either known or actual clinical evidence for autoimmune or internal disease was found, were included. Antinuclear and anti-smooth muscle antibodies (ANA and ASMA, respectively) were detected by immunofluorescence on rat organ sections and Hep 2 cells. Antibodies to liver-kidney-microsomes-1 (anti-LKM-1) and antimitochondrial antibodies (AMA) were detected and semiquantified by immunofluorescence. Additionally, anti-LKM-1 and AMA were determined by ELISA and Western blot. Antibodies against soluble liver antigens (anti-SLA) were quantified by ELISA. Sera with a titer of 1 : 40 or higher were classified as positive.

Sera of "healthy" adults displayed high frequencies of ANA and ASMA (28/111, 25%, and 48/111, 43%, respectively). Although no sex differences were found for ASMA, sera of healthy women tested more often positive for ANA (p < 0.01). Since at least one in three or four healthy individuals tested positive for ANA or ASMA, the positive predictive value of these autoantibodies is low, and clinical interpretation should include additional information.