The Anti-Saccharomyces cerevisiae IgG (ASCA-IgG) test detects the presence of IgG antibodies against Saccharomyces cerevisiae, a type of yeast commonly found in the gastrointestinal tract. This test is primarily used as a serological marker in the evaluation of inflammatory bowel disease (IBD), particularly in differentiating Crohn’s disease from ulcerative colitis.