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Test Code C1EST 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 Clinic 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 specimen collection, place the tube on wet ice.

2. Centrifuge at 4° C and separate serum from clot.

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) and Time(s) Performed


Test Classification

This test has been cleared, approved or is exempt 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


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 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

3. Frazer-Abel A, Sepiashvili L, Mbughuni MM, Willrich MA: Overview of Laboratory Testing and Clinical Presentations of Complement Deficiencies and Dysregulation. Adv Clin Chem. 2016;77:1-75

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: QUIDEL C1-Inhibitor Enzyme Immunoassay, 10165 McKellar Court, San Diego, CA, 12/2015)

Analytic Time

1 day

Reject Due To

Gross hemolysis OK
Gross lipemia OK
Gross icterus Reject
Other Heat-inactivated samples

Method Name

Enzyme Immunoassay (EIA)

Secondary ID