C1 esterase inhibitor test or C1-INH test is one of the tests carried out to check your complement protein levels. The complement system is part of your innate immune system. It consists of a set of nine proteins, numbered C1 through C9.They help your body recognize foreign cells that may cause disease. The C1-INH test can also be used to check causes of unexplained inflammation or swelling, known as edema and deficiency in C1 esterase inhibitor protein. The test includes functional C1 esterase inhibitor, C3 and C4 levels.