Supportive Data

In a study performed at Mayo Clinic, 173 serum samples submitted for clinical testing for anti-smooth muscle antibodies (anti-SMA), as performed by indirect immunofluorescence, were collected. These samples were subsequently tested using the anti-filamentous-actin (F-actin) antibody enzyme-linked immunosorbent assay (ELISA). By using the manufacturer's cut-offs for the 2 tests (negative at <20.0 units for the F-actin ELISA and <1:20 titer for the anti-SMA indirect immunofluorescence), the 2 tests had an overall concordance of 79.8%. In addition to the analytical concordance, patient histories were abstracted for diagnoses related to liver dysfunction. Of the 14 patients with autoimmune hepatitis, 13 were positive (≥20.0 units) for F-actin antibodies by ELISA, which corresponded to a sensitivity of 92.9%. Of the remaining 159 patients who had a diagnosis of something other than autoimmune hepatitis, 122 were negative (<20.0 units), which corresponded to a specificity of 76.7%. In comparison, at a clinical specificity of 76.1%, which is similar to the ELISA, the anti-SMA indirect immunofluorescence method had a significantly lower clinical sensitivity of 78.6%. Positivity for either anti-F-actin antibodies or anti-SMA improved the diagnostic sensitivity to 92.9%, although the specificity decreased to 66.0%. This data indicates that the ELISA for F-actin antibodies may have improved diagnostic utility in comparison to the anti-SMA by indirect immunofluorescence, although a combination of these tests may be useful for some patients.