C1 Esterase Inhibitor, Protein (C1-INH) Blood Test

The C1 Esterase Inhibitor, Protein (C1-INH) test measures C1-INH levels in a blood sample and help diagnose hereditary or acquired angioedema. The immune system protects us from pathogens (bacteria and viruses) by producing antibodies to combat them. In addition, a complement system is built into our immune system that helps the antibodies remove these pathogens. This complement system consists of nine proteins, labeled C1 through C9, that help our body identify infected cells that may cause disease. A deficiency of these proteins may be associated with certain diseases or disorders.

C1 Esterase Inhibitor (C1-INH) is a complement system protein that controls the C1 protein and is found in blood plasma or serum. Low C1-INH levels may cause two types of angioedema: hereditary angioedema and acquired angioedema. Hereditary angioedema primarily affects children and young adults under age 20. However, acquired angioedema mainly affects adults older than age 40. In addition, adults with acquired angioedema are much more likely to have other conditions, such as cancer or an autoimmune disease.

Signs or symptoms of both forms of angioedema include the following:

• Swollen face, feet, hands, and intestines
• Difficulty breathing
• Abdominal pain
• Nausea and vomiting

Common triggers for an angioedema attack may include:

• Anxiety
• Stress
• Minor trauma
• Surgery
• Illnesses such as cold, flu, or other viral infections

Individuals may order this test to help diagnose angioedema, manage treatment, or to help screen for other autoimmune diseases. Contact your doctor or healthcare provider if you have significant concerns or questions about your recent lab results.