One of the tests used to determine your complement protein levels is the C1 esterase inhibitor test, often known as the C1-INH test. Your innate immune system includes the complement system. It is made up of a group of nine proteins with the letters C1 through C9. They aid your body in identifying foreign cells that might be disease-causing. Edema and a lack of C1 esterase inhibitor protein are two additional conditions that can be investigated with the C1-INH test. Functional C1 esterase inhibitor, C3 and C4 levels are tested.