C3 diagnostic Test

Complement 3 (C3) is one of the most important proteins in the complement system, which is a group of proteins that play a crucial role in the immune response and in the clearance of immune complexes. The complement system is essential for innate immunity and aids in the adaptive immune response. It helps in lysing of microbial cells, promotes phagocytosis, and contributes to inflammation. C3 is central to the complement activation pathways - the classical, alternative, and lectin pathways.

C3 is pivotal in the complement system. When the complement system is activated by one of the pathways, C3 is cleaved into C3a and C3b. C3b aids in the opsonization of pathogens, which enhances phagocytosis by immune cells. C3a is an anaphylatoxin which is involved in inflammation.

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The measurement of C3 levels in the blood is mainly used to help diagnose conditions that cause inflammation and to monitor disease activity and the effectiveness of treatment. It can be particularly helpful in the diagnosis and monitoring of certain autoimmune diseases such as lupus (SLE). Low levels of C3 can be indicative of a consumption of complement due to the ongoing immune complex formation and clearance, as is often seen in active lupus.

Blood is usually drawn from a vein in the arm. The skin is cleaned with an antiseptic, and a tourniquet is applied above the injection site to slow down blood flow, which allows blood to be drawn more easily. The patient might feel a moderate sting or pinch. The blood sample is then sent to the laboratory for analysis.

• Test Name C3
• Sample Type Blood
• Preparations Required No special preparation is required for this test.
• Report Time 4 hours

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Normal ranges for C3 can vary between laboratories but are usually around 90-180 mg/dL.

• Decreased C3 Levels: Often seen in conditions where there’s excessive activation of the complement system. Conditions that can lower C3 include autoimmune disorders like SLE, kidney diseases such as post-infectious glomerulonephritis, and infections like sepsis.
• Increased C3 Levels: Sometimes, an increased level can be seen in acute inflammatory conditions since C3 is an acute-phase protein. This might also be seen in some cancers.
• Autoimmune Diseases: In diseases like SLE, the immune system attacks normal tissues as if they were foreign. During this process, immune complexes are formed which can deposit in tissues. The complement system, including C3, is involved in the clearance of these complexes.
• Infections: During severe infections like sepsis, the complement system is activated as part of the body's defense mechanism.
• Kidney Diseases: In certain kidney diseases, immune complexes get deposited in the kidney, leading to complement activation and low C3.
• Genetic Deficiencies: Very low levels might be due to a genetic deficiency of C3, which is rare but can cause increased susceptibility to infections.