C1 Esterase Inhibitor (Quantitational and Functional Level)

Immunology

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Description

C1 esterase inhibitor is an alpha-2 globulin serpin inhibitor. In its composite role as inhibitor of the recognition unit of the classical complement pathway, the coagulation and the kinin systems, C1 inhibitor is a major regulatory protein in the inflammatory response [1]. Hereditary angiodema ( HAE ) is an autosomal dominant condition, caused by deficiency of C1 esterase inhibitor. It is the commonest of the inherited complement component deficiencies with an incidence is in the order of 1:50,000 [2]. Two main forms of the inherited deficiency exist. In HAE type 1 both quantitative and functional C1 inhibitor levels are decreased as a results of ineffective protein secretion due to gene mutations. In HAE type 2, which accounts for 15% of cases, the C1 inhibitor quantitation can be either normal or elevated by the antigenic assay but have absent functional activity due to the secretion of a non-functional protein [1,2]. Acquired C1 inhibitor deficiency is a rare form, presenting for the first time in adult life. All reported cases have been secondary to lymphoma or myeloma, and full evaluation of the serum and urine immunoglobulins is indicated in these cases. In both the hereditary and aquired forms the C4 level is usually low but the C3 is normal [3]. More recently a third type of hereditary angioedema has been described. This oestrogen-dependent condition has mainly been observed in women but does not result in abnormally low functional or quantitative C1 inhibitor levels [4].

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Indications

Investigation and monitoring of Hereditary/Acquired Angioedema.

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Sample Type

2mL Serum ( Gel 5mL Yellow tube ) and 2mL EDTA Plasma. Requests from outside Sheffield: Freeze sample prior to dispatch and transport frozen sample at ambient temperature via Royal Mail or Courier ( dry ice not required ).

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Reference Range

Quantitation: 0.21 - 0.38 g/L.
Functional: Normal range: 70-150%.

Quantitative reference ranges established in house and by PRU collaboration.
Functional reference range established by manufacturer and verified in house.

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Turnaround Time

Within 2 days (quantitation) or Within 5 days (functional level)

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Testing Frequency

2-3 weekly

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External Notes

Quantitation & Function always measured together along with C3 and C4 quantitation. For functional assay send sample frozen ( samples may be sent liquid overnight, but to guarantee a valid result the sample should be sent frozen ). Details of clinical history and treatment should be given.

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References

PRU handbook of Clinical Immunochemistry. 9th Edition. 2007. [Ref 1]
Gompels MM, et al. C1 inhibitor deficiency: consensus document. Clin Exp Immunol. 2005. 139( 3 ):379-394. [Ref 2]
Markovic SN, et al. Acquired C1 esterase inhibitor deficiency. Ann Intern Med. 2000. 132( 2 ):144-150. [Ref 3]
Bork, et al. Hereditary angioedema with normal C1-inhibitor activity in women. Lancet. 2000. 356:213-217. [Ref 4]

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See Also

C3; C4

Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.