What does it mean if i have high serum iga levels?

How high?: Immunoglobulin A is present in serum (thus measurable by blood test), but its chief importance is in mucous membranes (respiratory tract and gut) and breast milk. Low levels can trigger infections like sinusitis and pneumonia. Mildly elevated levels can be normal, but higher values can be a sign of a form neoplasia (e.g. cancer) of plasma cells. See a hematologist/oncologist.