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Home > C1-Inhibitor (C1-INH) Function, Chromogenic Assay
Serum from a plain red top is the only acceptable sample type.
Gel barrier tubes are not acceptable.
Allow blood to clot at room temp or 37°C for 20 to 60 minutes. Centrifuge to thoroughly remove cells and immediately transfer cell-free serum to a fresh tube and freeze the cell-free serum on dry ice or at -70°C.
Preferred volume: 1 mL
Minimum volume: 250 µL serum, frozen
Send frozen serum Priority Overnight via FedEx and in a well insulated container on dry ice.
Frozen at -70°C: 1 year
Suggested additional testing:
If the C1-INH Function is low, a C1-INH level (Test Code: CEIQ) may aid in determining Type I versus Type II HAE.
If AAE is suspected, testing for auto-antibodies to C1-INH should be performed (Test Code: CEIAP).
3rd Tue of the month
Chromogenic Substrate Cleavage (DiaPharma, Technochrom®)
up to 4 weeks
C1-INH Chromogenic;C1-INH Function, European test;C1-INH Function, DiaPharma;C1-INH Function, technochrom;Complement;C1-esterase inhibitor function
The C1-inhibitor (C1-INH) was named for its role in inhibiting the enzymatic activity of C1r and C1s; thereby inhibiting activation of the classical pathway of complement. But C1-INH also has very important abilities to inhibit proteases in the fibrinolytic, clotting and kinin pathways. Specifically C1-INH inhibits the enzymatic activity of kallikrein, factor XIa, and Hageman factor (XIIa) of the coagulation and contact pathways. Failure of C1-INH to regulate these enzymes can result in life-threatening angioedema and a condition defined as Hereditary Angioedema of HAE. HAE Type I results from a missense mutation in the C1-Inhibitor gene that causes a premature stop in protein synthesis, so no secreted protein is produced. HAE Type I accounts for 85% of HAE cases and can be diagnosed by C1-INH levels. The Type II form, is a different missense mutation in the C1-Inhibitor gene, that results in a non-functional protein but normal or above normal levels of C1-INH. A third type has recently been described, HAE Type III. HAE Type III is not linked to mutations in C1-inhibitor. Instead they are finding mutations present in the Hageman factor and other targets of C1-INH. The mechanisms of this newest form of HAE are still under investigation.
Similar symptoms are manifested by Acquired Angioedema (AAE). AAE does not result from a genetic mutation but a depletion of effective C1-INH function through consumption of blocking of activity by an auto-antibody to C1-INH. In AAE-I, the associated disorders (usually lymphoproliferative malignancies) produce complement-activating factors, idiotype/anti-idiotype antibodies, or other immune complexes that destroy C1-INH function. In AAE_II a normal 105-kd C1-INH molecule is synthesized in adequate amounts but, because of an unknown event, a subpopulation of B cells secretes auto-antibodies to the C1-INH molecule.
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