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Laboratory studies

The results of laboratory studies are essential for differentiating between different forms of angioedema. The following laboratory parameters are obtained:

  • Concentration of C1-esterase inhibitor (C1-INH)
  • Activity of C1-INH (i.e. its ability to function correctly)
  • Concentration of complement factor C4
  • Concentration of complement factor C1q if there is suspicion of acquired angioedema

Example: In type I hereditary angioedema (HAE), both the concentration and activity of C1-INH are significantly reduced (usually to less than 30% of normal levels). In type II HAE, however, the concentration of C1-INH is normal or even elevated, but the activity of C1-INH is low.

The factors C4 and C1q are proteins belonging to the so-called complement system. The complement system is a kind of reaction chain in which a series of proteins (including C4 and C1q) are successively activated. These proteins play an important role in the body’s immune and inflammatory responses.

C1-esterase-inhibitor (C1-INH) blocks different steps in the reaction chain of the complement system. In patients with hereditary angioedema, however, these steps in the reaction chain are not adequately controlled due to the insufficient amount of correctly functioning C1-INH, leading to an increased consumption of C4. As a result, the concentration of the complement factor C4 declines. By contrast, the concentration of the complement factor C1q is normal in patients with hereditary angioedema, but low concentrations are seen in persons with other forms of bradykinin-mediated angioedema.

Characteristic changes in laboratory parameters in different forms of angioedema:

  C1-INH concentration C1-INH activity C4 C1q
HAE Typ I normal
HAE Typ II normal/↑ normal
AAE ↓/(rarely normal) ↓/(rarely normal)
Histamine-mediated Angioedema normal normal normal normal