Complement Component 3 (C3)
Alternate Names : C3
DefinitionThis is a blood test that measures one component of the complement cascade. Complement is a group of blood proteins that cause immune responses and
inflammation. The complement cascade is a series of reactions that take place in the blood. There are 9 major complement components, labeled C1 through C9. This test measures C3.
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Why is the Test Performed?
Complement activity (CH50, CH100, terminal complement component, or individual complement proteins) is measured to determine if complement is involved in the development of a number of diseases. Complement activity is also measured to monitor how severe a disease is or to determine if treatment is working. For example, patients with active lupus erythematosus may have low levels of C3 and C4, and these component levels may be watched as an indicator of disease activity.
Patients with gram negative septicemia and shock often have very low or no C3, and C3 is often also low in fungal infections and some parasitic infections such as malaria.
Red blood cells from patients with paroxysmal nocturnal hemoglobinuria (PNH) carry more C3 than do normal cells.
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