Diagnostic Performance of an Anti‐Actin Autoantibody Binding Enzyme Immunodot Blot in Autoimmune Hepatitis Type 1

Background A serologic hallmark of autoimmune hepatitis (AIH) type 1 are anti‐smooth muscle autoantibodies (ASMA) with specificity for filamentous actin (F‐actin; AAA (anti‐actin antibodies)), traditionally detected by indirect immunofluorescence (IFT) using rat liver, kidney, and stomach tissue sections as substrates. However, IFT is a subjective method requiring an experienced investigator. Therefore, a more objective technique for the detection of AAA may be a helpful diagnostic tool. Methods In a retrospective study with cross‐sectional design, we evaluated AAA detected by an enzyme immunodot blot (IDB; Liver5 IgG BlueDot, D‐tek, Mons, Belgium). Serum samples of patients with AIH type 1 ( n = 47) and specified controls ( n = 142) were included. For comparison, standard IFT was applied to rat LKS (liver, kidney, stomach) triple tissue sections. Results IDB readings were done by two independent investigators (92% concordance). The diagnostic sensitivity of the AAA‐IDB was 70%, compared to 51% of AAA‐IFT (n.s.). The diagnostic specificity of AAA‐IDB was significantly lower compared to AAA‐IFT (76% vs. 94%; P < 0.0005). Correspondingly, the positive predictive value (49% vs. 75%; P < 0.05) and positive likelihood ratio (2.9 vs. 8.5) differed significantly. Neither prescreening for ANA or ASMA, nor the exclusion of infectious hepatopathies resulted in a significantly better diagnostic performance of the IDB. Conclusion Compared to standard IFT, testing for AAA via IDB did not result in a significantly better diagnostic performance for AIH type 1. A blot with higher antigen binding specificity may be more functional.