Immunoblot assay shows comparable accuracy to ELISA in detecting anti-F-actin antibodies for autoimmune hepatitis type 1

Autoimmune hepatitis type 1 (AIH-1) is a rare but serious liver disease characterized by specific autoantibodies, including those against filamentous actin (F-actin). Traditional testing relies on indirect immunofluorescence (IIF) for smooth muscle antibodies (SMA), but this method lacks disease specificity. More recent solid-phase immunoassays, such as ELISA, have been adopted into diagnostic guidelines. This study investigated the diagnostic performance of an immunoblot-based solid-phase assay for F-actin and compared it to ELISA.

A total of 86 serum samples were analyzed from three patient groups: AIH-1 (14 patients), other liver disorders (38 patients), and unrelated non-liver conditions (34 patients). Samples were tested with both ELISA and an immunoblot assay, with immunoblotting detecting 16 positives (19%) and ELISA detecting 24 (28%). Diagnostic performance for immunoblotting included 50% sensitivity, 87.5% specificity, 43.8% positive predictive value, 90% negative predictive value, and 81.4% overall accuracy—figures comparable to ELISA. Receiver operating characteristic (ROC) analysis showed no significant difference between the two methods (AUC 0.77 vs. 0.82).

While immunoblotting demonstrated lower sensitivity than ELISA, it provided higher specificity and equivalent accuracy. Additionally, immunoblot assays offer the advantage of testing for multiple liver-related autoantibodies in one run, potentially increasing diagnostic efficiency in complex cases. ELISA, however, remains preferable for monitoring antibody titers over time.

The study concludes that immunoblot assays could be a reliable alternative to ELISA for detecting anti-F-actin antibodies, particularly as confirmatory tests when SMA is detected by IIF. However, due to limitations such as small sample size and retrospective design, larger prospective studies are needed before immunoblotting can be routinely implemented in clinical practice.