The Galactomannan (Aspergillus Antigen) test is a laboratory assay that detects galactomannan, a polysaccharide component of the cell wall of Aspergillus species, in blood or other body fluids. It is primarily used to aid in the early diagnosis of invasive aspergillosis, a serious fungal infection that commonly affects immunocompromised individuals. Detection of galactomannan supports timely antifungal therapy and monitoring of disease progression.