Upon reimaging after the abdominal pain has resolved, complete remission of abnormal findings may support the diagnosis of HAE.76 Determining serum levels of C4 constitutes the principal screening test for HAE.8,9,11 C4 levels are persistently low in most individuals with HAE due to C1-INH deficiency, although a small subset of patients demonstrates only low C4 levels during a symptomatic episode. Here, C4A is linked to hereditary angioedema.