The S-IgA test checks the levels of antibodies called immunoglobulins in your bloodstream. Antibodies are proteins made by your immune cells to fight off pathogens like bacteria, viruses, and mold but also to food proteins. The immunoglobulin test can show whether there's a problem with your immune system.
IgA antibodies are found in the mucous membranes of the lungs, sinuses, stomach, and intestines. They are also found in fluids produced by these membranes (saliva, tears, and blood). Most S-IgA is produced by the gastrointestinal barrier. IgA antibodies constitute 10 to 15% of the total antibodies.
Read more about the S-IgA blood test.