C1 Inhibitor, Protein and Functional Tests

The C1 Inhibitor, Protein test (test code 298) measures the concentration of the C1 esterase inhibitor protein using a fixed rate time nephelometry method. The C1 Inhibitor, Functional test (test code 297) measures the relative functionality of an individual’s C1 esterase inhibitor protein using an enzyme immunoassay. Both tests may be helpful in the diagnosis of hereditary angioedema (HAE). HAE is an autosomal dominant genetic disorder that manifests in 3 ways:

• Type I is the most common type of HAE, affecting about 85% of patients.¹ It is caused by mutations in the SERPING1 gene and is characterized by low levels (<11 ng/mL) of the protein and normal (>68%) protein function.
• Type II affects about 15% of HAE patients¹ and is also caused by SERPING1 mutations. Concentrations of the C1 inhibitor protein are normal (11-26 ng/mL), but the protein is dysfunctional (functional activity <40%).
• Type III is a rare type of HAE² that is associated with mutations in the F12 gene, which encodes the coagulation protein factor XII. HAE type III symptoms are exacerbated by pregnancy and oral contraceptives. The C1 esterase inhibitor protein concentration is typically normal, as is the protein function.