B-055 Comparison of Sensitivity Between Tissue Anti-Transglutaminase and Anti-Endomysium IgA and IgG in Serological Screening for Celiac Disease in a Large Clinical Laboratory in Brazil

Abstract

Abstract Background Celiac Disease (CD) is a genetic and autoimmune disorder characterized by permanent intolerance to gluten found in foods, resulting in small intestine injury in children and adults. Anti-tissue transglutaminase (anti-tTG) and anti-endomysium (anti-EM) antibodies are important serological markers of this disease. The aim was to analyze the analytical sensitivity of these markers in a large-scale Clinical Laboratory routine. Methods We employed a pure sample and a series of dilutions in the analysis of the functional sensitivity of each marker (anti-tTG IgA/IgG and anti-EM IgA/IgG) and a database survey of a large Clinical Laboratory in Sao Paulo/Brazil, from January to December 2021, analyzing 60 000 samples with concomitant results of anti-tTG IGA and anti-EM IgA and 7075 samples with results of anti-tTG IgG and anti-EM IgG, from patients with no defined clinic condition. The anti-tTG tests were performed by fluorescence enzyme immunoassay (FEIA) and the anti-EM tests by indirect immunofluorescence (IFI), with an initial dilution of 1:10, following the manufacturer's recommendations. Results The determination of functional sensitivity by checking the maximum dilution of antibody detection showed higher sensitivity of the anti-tTG IgA and IgG test (dilution factor 0.3 for both) compared to the anti-EM IgA and IgG (dilution factor 0.7 for both). Of the 60 000 samples analyzed for IgA markers, 59 083 (98.5%) were negative for both tests. Of the remaining 917 samples (1.5%), 609 (66.4%) were positive for both anti-tTG IgA and anti-EM IgA, 308 (33.6%) were positive only for anti-tTG IgA, and we did not observe any sample anti-tTG IgA negative with anti-EM IgA positive. Of the 7075 samples analyzed for IgG markers, 7032 (99.4%) were negative for both tests. Of the remaining 43 samples (0.6%), 18 (41.9%) were positive for anti-tTG IgG and anti-EM IgG, 14 (32.6%) were positive only for anti-tTG IgG, and 1 (2.3%) were positive only for anti-EM IgG. Conclusion The study showed greater sensitivity of anti-tTG compared to anti-EM for both IgA and IgG, in agreement with the literature data. The anti-tTG IgA test, in individuals without immunoglobulin A (IgA) deficiency, is recommended as the initial test in suspicion of celiac disease by current scientific guidelines on celiac disease. Based on our findings and literature data, in individuals with IgA deficiency, we suggest a screening using two automated IgG markers, tTG IgG and deamidated gliadin IgG (DG IgG). In addition to the lower sensitivity of anti-EM, indirect immunofluorescence (IFI), compared to the fully automated FEIA method, is a more subjective, observer-dependent, and labor-intensive methodology to be used as screening in large-scale Clinical Laboratory routines.