The clinical significance of anticytoplasmic antibodies found on fluorescent antinuclear antibody testing.

We evaluated anticytoplasmic antibodies (FACA) found on immunofluorescent antinuclear antibody tests (FANA). Of 1830 sera submitted to our laboratory for FANA testing, we found a 2.7% incidence of FACA as compared to a 21.5% incidence of FANA. Patients with FACA had rheumatologic and other systemic diseases closely resembling those present in controls with FANA, indicating that FACA provide a pathologic marker independent of FANA. Among FACA+ patients studied further, 59% were found to have serum antibodies to mitochondrial (Mit) and/or smooth muscle (SMus) antigens, largely in the absence of liver disease. By contrast, sera from FANA+ controls lacked anti-Mit and anti-SMus antibodies, but did contain antibodies to SSA, SSB, dsDNA, Sm, and RNP in much higher frequency than FACA+ sera.