The Endomysial Antibody (EMA) IgG test is used primarily to screen for celiac disease, particularly in cases where IgA deficiency is suspected. This test detects the presence of IgG antibodies against endomysium, a tissue found in the intestinal lining, which can indicate autoimmune activity. A positive result suggests a higher likelihood of celiac disease or gluten sensitivity, while a negative result may rule it out. It's generally used alongside other celiac tests for a more comprehensive diagnosis.