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.
C1 esterase inhibitor
Ambient (8 - 24 degrees Celsius)
Abnormally low results are consistent with a heterozygous C1 esterase inhibitor deficiency and hereditary angioedema.
Fifteen percent of hereditary angioedema patients have a normal or elevated level but nonfunctional C1 esterase inhibitor protein.
> 0.18 g/L
Nephelometric immunoassay on Siemens BNII
$42.65 (Exclusive of GST)
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.
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