C1-esterase inhibitor


SynonymC1-Inactivator, C1-Inhibitor , C1-INH
Molecular mass110.000 Da
Half-Life64 h
Plasma concentration

0.18 - 0.22 g/l or

1.7 - 2.0 μmol

Normal range70 - 130%

As an inhibitor of the active subcomponent of the first complement factor, the C1-Inhibitor is assigned to the complement system. The contact activation is inhibited by inhibition of factors XIIa and XIa. The inhibition of fibrinolysis connected therewith is accelerated by the direct inhibition of kallikrein and plasmin by the C1-Inhibitor as well as by the elimination of the plasmin mediated activation of prourokinase.

Clinical significance

Due to uncontrolled complement activation in C1 inhibitor deficiency (≤ 25% of normal), recurrent angioedema of the skin, gastrointestinal tract and trachea is observed. Hereditary angioedema (HAE) is caused by a synthesis defect of the C1-inhibitor (type I) or functional insufficiency with normal protein concentrations (type II). The acquired oedema (AAE) type I is a disease of the B-cell system, such as chronic lymphatic leukaemia. Type II of an AAE is caused e.g. by an inactivation of the C1-inhibitor through autoimmune antibodies of the IgG class.


  • Suspected hereditary complement defect
  • Acquired C1-esterase inhibitor deficiency


  1. Bork K. Angioödeme durch C1-Esterase-Inhibitor-Mangel. Gelb. H. 118, 1990.
  2. Markovic SN et al. Acquired C1 esterase inhibitor deficiency. Ann Intern Med 132, 144-150, 2000.
  3. Wiman B, Nilsson T. A new simple method for determination of C1-esterase inhibitor activity in plasma. Clin Chim Acta 128, 359-366, 1983.
  4. Bowen B et al. A review of the reported defects in the human C1 esterase inhibitor gene producing hereditary angioedema including four new mutations. Clin Immunol 98, 157-163, 2001.
  5. Crowther M, Bauer KA, Kaplan AP. The thrombogenicity of C1 esterase inhibitor (human): review of the evidence. Allergy Asthma Proc. Nov-Dec 35(6), 444-53, 2014.
  6. Acquired C1 esterase inhibitor deficiency via bradykinin-mediated angioedema: Four cases. Ann Dermatol Venereol. Apr 16. Pii S0151-9638(18), 30132-7, 2018.

Test kit

Chromogenic Assay

Technochrom® C1-Esterase Inhibitor