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Test Identifier Information

Registration CodeCIN


Diagnostic Use / Indications

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. 

External Price$39.81(Exclusive of GST)

Specimen Collection

Pre-Testing Requirements


Patient Specimen5 mL clotted blood (Red)
Paediatric Specimen0.5 mL clotted blood (Red)
Sample Delivery to LabAmbient

Instructions for Referral to CHLabs

Aliquot Instructions200 uL serum - minimum 1 mL serum - preferred Store in fridge
Aliquot Transport to CHLAmbient

CHLabs Laboratory

DepartmentBiochemistry - Protein Laboratory
Contact Details Email Email
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Contact Phone Number(03)3640334 | x80334
Test AvailabilityBatched weekly
Turnaround Time1 - 2 weeks
Reference Interval

Normal range >18g/L


C1 Inhibitor
Hereditary angioedema is a rare disorder resulting from an autosomal dominant deficiency of C1 inhibitor. This deficiency produces an uncontrolled activation of the early components of the classic complement system, with generation of a kinin-like substance that causes recurrent angioedema of the gastrointestinal and genitourinary tracts, and the larynx. The subcutaneous and submucosal oedema is usually harmless but when the larynx is involved death may occur due to respiratory obstruction and asphyxiation. Two variants of the disease exist. In 85% of cases the C1 inhibitor levels are typically 35% - 50% of the 99th percentile of the healthy population. (Type I). In the remaining 15%, normal concentrations of a functionally abnormal protein are produced (Type II). Typically C4 levels will be low during and between attacks of angioedema resulting from both type I and type II deficiency. Rarely, acquired C1 inhibitor deficiency can arise in a patient with lymphoma or in association with an autoimmune disease. Unlike the hereditary form where C4 levels are low and C1 levels normal, in the acquired form low levels of both C1 and C4 occur.

Additional Information

C3 and C4 analysis performed on all requests, unless results provided. 85% of hereditary angioedema cases have a C1 inhibitor level of 35% - 50% of normal. However hereditary angioedema is unlikely in the presence of a normal C4 level despite a low C1 level.

Delphic Number Test Number6869

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