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Test Code FC1EQ C1 Esterase Inhibitor, Functional Assay, Serum

Reporting Name

C1 Esterase Inhib, Functional

Useful For

Diagnosing hereditary angioedema and for monitoring response to therapy

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Serum Red


Specimen Required


Patient Preparation: Patient should be fasting.

Collection Container/Tube: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions:

1. Immediately after drawing the specimen, place the tube on wet ice.

2. Spin down and separate serum from clot.

3. Freeze specimen within 30 minutes.


Specimen Minimum Volume

0.1 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Red Frozen 6 days

Reference Values

>67% normal (normal)

41-67% normal (equivocal)

<41% normal (abnormal)

Day(s) and Time(s) Performed

Varies

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

83520

LOINC Code Information

Test ID Test Order Name Order LOINC Value
FC1EQ C1 Esterase Inhib, Functional 48494-4

 

Result ID Test Result Name Result LOINC Value
81493 C1 Esterase Inhib, Functional, QN 48494-9

Clinical 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 Hageman factor (factor XIa), 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.

Interpretation

Hereditary angioedema (HAE) can be definitely diagnosed by laboratory tests demonstrating a marked reduction in C1 inhibitor (C1-INH) antigen or abnormally low functional C1-INH levels in a patient's plasma or serum that has normal or elevated antigen.

 

Nonfunctional results are consistent with HAE.

 

Patients with current attacks will also have low C2 and C4 levels due to C1 activation and complement consumption.

 

Patients with acquired C1-INH deficiency have a low C1q in addition to low C1-INH.

Clinical Reference

1. Stoppa-Lyonnet D, Tosi M, Laurent J, et al: Altered C1 inhibitor genes in type I hereditary angioedema. N Engl J Med 1987;317:1-6

2. Frigas E: Angioedema with acquired deficiency of the C1 inhibitor: a constellation of syndromes. Mayo Clin Proc 1989;64:1269-1275

Analytic Time

1 day

Reject Due To

Hemolysis

Mild OK; Gross OK

Lipemia

Mild OK; Gross OK

Icterus

Mild OK; Gross OK

Other

Serum gel tube

Method Name

Enzyme Immunoassay (EIA)