Test Details: C1 esterase inhibitor is important in regulating the immune system. C1 esterase inhibitor test checks the level of a substance called C1 esterase inhibitor in blood. This test is also used to assess for Hereditary angioedema. Symptoms of hereditary angioedema include swelling in feet, face, hands, airways and gastrointestinal tract; abdominal pain; nausea and vomiting.