From the Guidelines
A C4a (Complement component 4a) test is not directly mentioned in the provided evidence, however, the C4 (Complement component 4) test is discussed as a screening tool for hereditary angioedema (HAE) and other conditions.
Key Points
- The C4 test is used to measure the level of C4 in the blood, which can be decreased in patients with HAE or other conditions such as systemic lupus erythematosus (SLE) 1.
- A low C4 level is generally present in patients with C1INH deficiency, which is a common cause of HAE 1.
- The C4 test is recommended as the best initial screening test to exclude a diagnosis of HAE 1.
- C4 levels can be normal in patients with HAE who are already being treated, or in patients with other conditions such as ACE-I-associated angioedema 1.
Clinical Use
- The C4 test is used in the diagnosis and monitoring of patients with HAE, SLE, and other conditions that affect the complement system 1.
- A C4 test can help to distinguish between different types of angioedema, such as HAE and ACE-I-associated angioedema 1.
- The C4 test can also be used to monitor the effectiveness of treatment in patients with HAE or other conditions that affect the complement system 1.
From the Research
C4a Test Overview
- The C4a test is used to measure the levels of C4a, a fragment of the complement component C4, in the blood or other bodily fluids 2, 3.
- C4a is released from complement component C4 upon activation of the complement system's classical and lectin pathways, which are important constituents of innate immune surveillance 2.
Clinical Significance
- Elevated plasma C4a levels have been linked to disease activity in multiple sclerosis, suggesting a role for complement activation in the pathogenesis of the disease 3.
- C4a has also been shown to mediate effector functions by binding to protease-activated receptors 1 and 4, leading to increased endothelial permeability and stress fiber formation 2.
Measurement and Analysis
- C4a levels can be measured using various techniques, including isoelectrofocusing and chemical reactivity of activated forms 4.
- The ratio of C4A to C4B isotypes can also be calculated to detect deficiencies in these isotypes, which may be associated with pathological immune processes 5, 6.
Complement Component C4
- Complement component C4 is an important plasma protein that plays a major role in the human defense mechanism against infectious diseases and inflammatory processes 5.
- The C4A and C4B genes, which encode the two isoforms of complement 4, are located in the RP-C4-CYP21-TNX module and have variable copy numbers among individuals 5.