C1 Esterase Inhibitor (C1s), Serum


C1 Esterase Inhibitor is a heavily glycosylated single-chain polypeptide acute phase protein that belongs to the superfamily of serine proteinase inhibitors (serpins), which includes, α1-antitrypsin, anti-thrombin, and plasminogen activator inhibitor type I. It is the only known inhibitor of the activated serine proteinases C1s and C1r from the classical pathway of complement, and is a major inhibitor of activated factor XII (FXIIa) from the contact system. In addition, it functions as an inhibitor of kallikrein and activated factor XI (FXIa) thus; it is an important regulator of inflammatory reactions and of the intrinsic pathway of coagulation


Hereditary angioedema, characterised by recurrence of cutaneous and mucous membrane swellings in any part of the body (more commonly the extremities but may also involve the upper respiratory tract, including the tongue, pharynx, and larynx) and abdominal pain is inherited in an autosomal dominant manner. Symptoms of hereditary angioedema usually appear early in life. The diagnosis is classically confirmed by low C1s and C4 levels.

Sample Type, Quantity & Conditions

1 ml Serum Frozen

Special Precautions

Freeze immediately. Cyclosporin-A treatment may inhibit the enzyme.

Normal Range

19.5 - 34.5 mg/dL 0.195 - 0.345 g/L

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