Update Type: Replacement Test
Test Updated: 08/24/2022
Test Overview
Test Methodology

Enzyme Immunoassay (EIA)

Test Usage

The diagnosis of C1 esterase inhibitor deficiency (hereditary angioedema) or monitoring response to therapy. If C1 Esterase Inhibitor Quantitation is low, it is not necessary to do the functional assay, as it will also be low.

Reference Range *

Normal: >67%, Equivocal: 41 - 67%, Abnormal: <41%

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Details
Days Set Up
Analytic Time

2 - 6 days

Soft Order Code
MiChart Code
C1 Esterase Inhibitor, Functional
  • FC1EQ
  • Hereditary Angioedema (HAE)
  • HAE (Hereditary Angioedema)
  • Complement C1 Esterase Inhibitor, Functional
  • Functional C'1 Esterase
  • C1 Esterase Inhib, Functional
Reference Laboratory
Mayo C1INF
Special Testing
Specimen Requirements

A fasting specimen is preferred but not required. Collect specimen in a red top tube. (SST is acceptable) Immediately place on wet ice. Centrifuge, aliquot serum into a plastic vial and freeze immediately, within 30 minutes. Hemolytic or thawed specimens are unacceptable.

Special Handling

Place specimen on wet ice immediately following collection. Must arrive in lab or aliquot and freeze within 30 minutes.

Fasting Specimen
A fasting specimen is preferred but not required.
Normal Volume
1 mL serum
Minimum Volume
0.4 mL serum
Storage Temperature
Rejection Criteria
Green top tube not acceptable.
Additional Information

C1 inhibitor (C1-INH) is a multispecific, protease inhibitor that is present in normal human plasma and serum, and which regulates enzymes of the complement, coagulation, fibrinolytic, and kinin-forming systems. The enzymes (proteases) regulated by this protein include the C1r and C1s subunits of the activated first component of complement, activated XIIa, kallikrein (Fletcher factor), and plasmin. A deficiency of functionally active C1-INH may lead to life-threatening angioedema. Two major forms of C1-INH deficiency have been reported: the congenital form, termed hereditary angioedema (HAE), and the acquired form that is associated with a variety of diseases, including lymphoid malignancies. HAE is characterized by transient but recurrent attacks of nonpruritic swelling of various tissues throughout the body. The symptomatology depends upon the organs involved. Intestinal attacks lead to a diversity of symptoms including pain, cramps, vomiting, and diarrhea. The most frequent cause of death in this disease is airway obstruction secondary to laryngeal edema occurring during an attack. There are 2 types of HAE that can be distinguished biochemically. Patients with the more common type (85% of HAE patients) have low levels of functional C1-INH and C1-INH antigen. Patients with the second form (15% of HAE patients) have low levels of functional C1-INH but normal or increased levels of C1-INH antigen that is dysfunctional. The variable nature of the symptoms at different time periods during the course of the disease makes it difficult to make a definitive diagnosis based solely on clinical observation. Test sent to Mayo Medical Laboratories.

CPT Code
Fee Code