Optimising the diagnostic value of Anti-Saccharomyces cerevisiae-antibodies (ASCA) in Crohn's disease

Background/Aims. Anti-Saccharomyces cerevisiae-antibodies (ASCA) are used to discriminate Crohn's disease (CD) from ulcerative colitis (UC). ASCA tests are not standardised and different methods for ASCA detection exist. This study was undertaken to compare ASCA tests and to clarify their diagnostic value. Patients/Methods. One hundred and two sera from CD patients, 53 from UC patients, and 50 sera from normal controls were examined for ASCA IgA and ASCA IgG using four different ELISA (Aesku.lab, Inova, Euroimmun, and Medipan) and indirect immunofluorescence (Euroimmun). Sensitivity, specificity, and positive and negative predictive values (PPV and NPV) for CD in this population were determined. Agreement between tests was expressed by kappa statistics. Results/Findings. The presence of either ASCA IgA or ASCA IgG had a PPV between 77 and 88%. Only the combined presence of ASCA IgA and ASCA IgG had a specificity which was constantly above 90%. Sensitivity, specificity, PPV, and NPV were then: Inova: 53, 97, 95, and 68%; Euroimmun ELISA: 46, 97, 94, and 66%; Aesku.lab: 50, 97, 94, and 66%; Medipan: 30, 98, 94, and 59%; indirect immunofluorescence: 51, 97, 94, and 66%. Agreement between ELISA test results of the Aesku.lab, Euroimmun, Medipan IgA and Inova systems was good (kappa: 0.63-0.79); between the Medipan IgG ELISA or indirect immunofluorescence and the others, it was lower (kappa: 0.33-0.6). If both ASCA IgA and ASCA IgG were detected by indirect immunofluorescence as well as ELISA, specificity for CD increased to >99% at a sensitivity of 23-38%. Interpretation/Conclusions. The combined detection of ASCA IgA and ASCA IgG by indirect immunofluorescence as well as ELISA may optimise the discrimination of CD from UC.