C4a Level by RIA

Optimal Result: 0 - 2830 ng/mL.

C4a Level by RIA (Radioimmunoassay) is an important test in immunology, offering insights into the body's immune response, particularly in the context of inflammation and autoimmune disorders. The C4a component is a part of the complement system, a group of proteins in the blood that play a crucial role in the body's defense against infections and in the process of inflammation. When the complement system is activated in response to a threat like an infection, C4a is produced as a byproduct. Measuring the levels of C4a, therefore, can help in understanding if the complement system is overactive, which is often the case in autoimmune diseases or during certain allergic reactions.

The Radioimmunoassay (RIA) method used to measure C4a levels is a sensitive and specific technique. It involves using antibodies and radioactively labeled substances to detect and measure the concentration of C4a in the blood. This test is particularly useful in diagnosing conditions like systemic lupus erythematosus (SLE), where the complement system plays a significant role. Elevated levels of C4a might suggest active disease or an exacerbation in patients with SLE or other similar autoimmune conditions.

In addition to its use in autoimmune disorders, C4a levels can also be indicative of other conditions involving inflammation or immune response anomalies. For example, in cases of chronic fatigue syndrome, Lyme disease, or certain types of infections, abnormal C4a levels can provide valuable diagnostic information.

It's important to note that while the C4a Level by RIA is a powerful diagnostic tool, it should always be interpreted in the context of other clinical findings and tests. The results can vary depending on several factors, including the individual's overall health, the presence of other medical conditions, and specific laboratory techniques. Therefore, elevated or decreased C4a levels should be assessed by healthcare professionals who can consider the full clinical picture.


Margery-Muir AA, Bundell C, Wetherall JD, Whidborne R, Martinez P, Groth DM. Insights on the relationship between complement component C4 serum concentrations and C4 gene copy numbers in a Western Australian systemic lupus erythematosus cohort. Lupus. 2018 Sep;27(10):1687-1696. doi: 10.1177/0961203318787039. Epub 2018 Jul 24. PMID: 30041577.

Ittiprasert W, Kantachuvesiri S, Pavasuthipaisit K, Verasertniyom O, Chaomthum L, Totemchokchyakarn K, Kitiyanant Y. Complete deficiencies of complement C4A and C4B including 2-bp insertion in codon 1213 are genetic risk factors of systemic lupus erythematosus in Thai populations. J Autoimmun. 2005 Aug;25(1):77-84. doi: 10.1016/j.jaut.2005.04.004. PMID: 15998580.

Yang Y, Chung EK, Zhou B, Lhotta K, Hebert LA, Birmingham DJ, Rovin BH, Yu CY. The intricate role of complement component C4 in human systemic lupus erythematosus. Curr Dir Autoimmun. 2004;7:98-132. doi: 10.1159/000075689. PMID: 14719377.

Traustadóttir KH, Steinsson K, Erlendsson K. C4AQ0 superimposed on a primary defect increases the susceptibility to systemic lupus erythematosus (SLE) in a family with association between C4AQ0 and SLE. J Rheumatol. 1998 Nov;25(11):2118-25. PMID: 9818652.

Wu YL, Yang Y, Chung EK, Zhou B, Kitzmiller KJ, Savelli SL, Nagaraja HN, Birmingham DJ, Tsao BP, Rovin BH, Hebert LA, Yu CY. Phenotypes, genotypes and disease susceptibility associated with gene copy number variations: complement C4 CNVs in European American healthy subjects and those with systemic lupus erythematosus. Cytogenet Genome Res. 2008;123(1-4):131-41. doi: 10.1159/000184700. Epub 2009 Mar 11. PMID: 19287147; PMCID: PMC2709077.

What does it mean if your C4a Level by RIA result is too high?

Elevated levels of C4a, a fragment of the complement protein C4, can be a sign of increased immune system activity, often occurring in response to inflammation, infection, or autoimmune disorders. The complement system, which includes C4a, is part of the body's innate immune response, playing a critical role in defending against pathogens and clearing damaged cells. When C4a levels are high, it suggests that this system is highly active, which can occur in various contexts.

For instance, in autoimmune conditions like systemic lupus erythematosus (SLE), the immune system mistakenly attacks healthy tissues, triggering an inflammatory response and complement activation, leading to higher levels of C4a. Similarly, in cases of acute infections or tissue injury, the body's response to fight off the infection or heal the injury can result in increased C4a levels.

However, it's crucial to note that high C4a levels are not specific to any one disease but rather indicate an ongoing immune or inflammatory process. Elevated C4a can be seen in a wide range of conditions, from infections and autoimmune diseases to allergic reactions. The interpretation of C4a levels should always be done in the context of the overall clinical picture, including symptoms, other lab tests, and patient history. Therefore, increased C4a levels should prompt further investigation by healthcare professionals to determine the underlying cause and appropriate management.

In summary, elevated C4a levels are a marker indicating an active immune response, useful in diagnosing and monitoring various health conditions, but they should be interpreted alongside other medical information for accurate diagnosis and treatment planning.

What does it mean if your C4a Level by RIA result is too low?

Low levels of C4a, a fragment of the complement protein C4, can be indicative of various health conditions and immune system dysfunctions. The complement system, including C4a, plays a critical role in the body's defense mechanism against infections and in managing inflammation. When C4a levels are low, it may suggest a reduced ability of the immune system to respond to infections or clear damaged cells and tissues. This can be particularly relevant in autoimmune diseases, like systemic lupus erythematosus (SLE), where low levels of C4a are often associated with disease activity. In such cases, the immune system mistakenly attacks healthy tissues, and the complement system, including C4a, is consumed in the process, leading to lower levels in the blood.

Moreover, low C4a levels might also indicate a genetic predisposition to certain autoimmune conditions. Hereditary deficiencies in complement proteins, including C4a, can leave individuals more susceptible to autoimmune reactions. In addition to autoimmune conditions, low C4a levels can be found in other scenarios where the immune system is compromised or overactive, such as in certain infections or inflammatory conditions.

It's important to understand that low C4a levels are not a disease themselves but a marker that can help in diagnosing and understanding the underlying causes of certain health conditions. The interpretation of C4a levels should be done in conjunction with other clinical findings and tests, as the implications can vary depending on the overall health context and the presence of other medical conditions. Therefore, a comprehensive assessment by healthcare professionals is crucial to accurately determine the significance of low C4a levels in each individual case.

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