Screening for acquired or hereditary C1 inhibitor deficiency will now be undertaken with a functional C1 inhibitor assay and a C4 assay. If the C1 inhibitor functional assay is reduced, the C1 antigenic assay will be added to testing. If there is high suspicion about C1 inhibitor deficiency in spite of a normal C1 inhibitor functional assay, please contact the Immunology team at LabPLUS.
Sample needs to be separated and frozen within 1 hour of collection.
Place the yellow fluorescent sticker Urgent C1 Esterase Inhibitor label on the form at the time of blood collection. Ensure the yellow sticker is visible when form is placed in the biohazard bag.
Specimen Collected at Greenlane
Please spin and separate within 1 hour of collection. Prepare 2 aliquots and freeze specimen. Place the yellow fluorescent sticker Urgent C1 Esterase Inhibitor label on the form. Ensure the yellow sticker is visible when form is placed in the biohazard bag. Transport frozen aliquots to main lab.
3.5 mL SST Serum (Preferred) 4 mL Plain Serum Reference Intervals
Uncertainty of measurement: 18%
Age Range Either Sex All >= 68 Abnormal
Age Range Either Sex All < 40 Equivocal
Age Range Either Sex All 41 - 67 Turnaround Time: Between 1 week and 2 weeks Assay Method
ELISA assay using the Quidel C1-Inhibitor enzyme Immunoassay kit.
Diagnostic Use and Interpretation
C1 inhibitor levels are reduced in cases of hereditary angioedema. In this condition, 85% of patients will have decreased antigenic and functional C1 inhibitor levels, whereas 15% will have a dysfunctional protein (normal or high antigenic assay, low functional assay).
The C4 component of complement is almost invariably low in cases of hereditary angioedema, and C2 is low during acute attacks.
C1 Esterase Inhibitor deficiency causes angioedema. The C1 Esterase Inhibitor deficiency may be genetic (hereditary angioedema) or aquired. Hereditary angioedema may be caused by an absence or a dysfunctional C1 Esterase Inhibitor. Most patients with C1 Esterase Inhibitor deficiency have reduced C4 levels. A normal C4 level makes C1 Esterase Inhibitor deficiency unlikely. Note that patients with type 3 HAE may have normal C4 levels.
Acquired C1 inhibitor deficiency can occur rarely in SLE and B cell lymphomas. Acquired C1 inhibitor deficiency can be distinguished from the hereditary form by measuring C1q levels which are low in the acquired form but normal in the inherited.
For further information contact the laboratory (09) 307 4949 ext 22000 or:
Associate Professor Rohan Ameratunga , Immunopathologist: Locator 93-5724
Or the LabPLUS Immunology Team
Specimen Transport Instructions for Referring Laboratories
Specimens for C1 Esterase Inhibitor functional activity MUST be separated and frozen within 1 hour and sent frozen.