Test Code LAB10251 C1 Esterase Inhibitor, Functional Assay, Serum
Reporting Name
C1 Esterase Inhib, FunctionalUseful For
Diagnosing hereditary angioedema and for monitoring response to therapy
Performing Laboratory

Specimen Type
Serum RedSpecimen Required
Patient Preparation: Patient should be fasting.
Supplies: Aliquot Tube, 5 mL (T465)
Collection Container/Tube: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
Collection Instructions:
1. Immediately after specimen collection, place the tube on wet ice.
2. Centrifuge at 4° C and aliquot serum into a 5-mL plastic vial.
3. Freeze specimen within 30 minutes.
Specimen Minimum Volume
0.1 mL
Specimen Stability Information
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Serum Red | Frozen | 28 days |
Reference Values
>67% normal (normal)
41-67% normal (equivocal)
<41% normal (abnormal)
Day(s) Performed
Varies
Test Classification
This test has been cleared, approved, or is exempt by the US 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 | 48494-9 |
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.
Method Description
Patient serum is mixed with C1 inhibitor (C1-INH) reactant (biotinylated, activated C1s). Functionally active C1-INH will bind to the biotinylated C1-INH reactant to form complexes. An aliquot of the serum mixture containing biotinylated C1-INH reactant is added to microtiter wells precoated with avidin. The C1-INH reactant:C1-INH complexes bind to the wells. C1-INH is detected using a horseradish peroxidase (HRP)-conjugated antibody against C1-INH. Color generation is accomplished by incubation with a chromogenic substrate. After incubation the enzyme reaction is stopped chemically, and the color intensity is measured spectrophotometrically. The color intensity is proportional to the concentration of functional C1-INH present in the serum.(Package insert: C1-Inhibitor Enzyme Immunoassay, Quidel; 12/2015)
Report Available
3 to 5 daysReject Due To
Gross hemolysis | OK |
Gross lipemia | OK |
Gross icterus | Reject |
Heat-inactivated samples | Reject |
Method Name
Enzyme Immunoassay (EIA)