Immunofluorescence assay for antinuclear factor: a nonspecific test in hospitalized medical patients

Serum from 149 randomly selected hospitalized medical patients was tested for the presence of antinuclear factor (ANF) by the conventional immunofluorescence technique. Patients with positive and negative results were then compared as to clinical history, particularly previous drug exposure, physical findings, and levels of C-reactive protein and immune complexes in the serum. The frequency of ANF positivity was found to be very high (23%). Although the presence of ANF was significantly correlated (P less than 0.02) with a higher age, it was not significantly related to any other clinical or laboratory feature assessed. It was concluded that ANF testing cannot serve as a blind diagnostic screening tool for connective tissue diseases because of its nonspecificity.