Aspergillus is a common type of fungus that grows on decaying vegetation, such as compost heaps and fallen leaves. It can also be found in air-conditioning systems and hospitals. Immunoglobulin A (IgA, also referred to as sIgA) is an antibody that plays a crucial role in the immune function of mucous membranes. The amount of IgA produced in association with mucosal membranes is greater than all other types of antibody combined. Aspergillus precipitin detects the type and quantity of specific Aspergillus antibodies in the blood. Antibodies are immunoglobulin proteins made by the immune system in response to harmful substances called antigens. An antigen is a substance that your body recognizes as a threat. No utility has been found for the detection of IgA antibodies to fungi.