The Significance of Complement C3 and 4 High Results

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What is the Complement System?

The complement system is a group of proteins produced in the liver. They circulate in the blood as part of the body’s immune defenses. Their main function is to destroy foreign invaders like viruses and bacteria by attacking their cell membrane. They also recruit other cells of the immune system to go to the site of injury and enhance the engulfment of these foreign bodies. There are nine principal complement components present in the blood and they are referred to as C1 up to C9. They act following a certain pattern known as the complement cascade, where each one is important. There are also other subcomponents and inhibitors of the complement system which assist and regulate the actions of the principal complements.

There are available test that measures the activity of the whole complement system, such as the CH100 and CH50. There are also specific blood test that measures each separate complement component. Most commonly requested specific complement component test are for the measurement of C3 and C4.

What is C3 and C4?

C3 is a test for the measurement of its action and functions in the blood. The normal value for C3 is 75 to 135 mg/dl. C4 is also a test for the measurement of the action and function of C4 in the blood. Its normal value is 12 to 72 mg/dL in males and 13 to 75 mg/dL in females. The test is usually done by extracting an adequate amount of blood in the arm vein. The blood sample is then sent to the laboratory for the analysis of these blood components.

Why is C3 and C4 Done?

C3 and C4 are the most common complement components measured. Their activities are often measured to verify the extent of a disease or find out if the treatment is working. Physicians usually request for complement tests in order to monitor patients with autoimmune diseases and to follow up the efficacy of their treatments. C3 and C4 tests are also done in cases of fungal infections, gram-negative septicemia, paroxysmal nocturnal hemoglobinuria and malaria. They may also be needed to evaluate patients with unexplainable cases of edema and inflammation, and in those manifesting symptoms of SLE or systemic lupus erythematosus as well as other autoimmune disorders.

What is the Significance of Complent C3 and 4 High Results?

During acute and chronic inflammatory processes, these complement proteins together with other proteins of the body have increased level of activities thus their values are usually increased. When the underlying problem has been resolved, their values typically return to its normal level. Persistently high C3 and C4 results may be associated with ulcerative colitis and cancer.

There are several diseases, however, which can decrease the results for C3 and C4 . These include hepatitis, kidney transplant rejection and malnutrition.


Lab Test Online: Complement

MedlinePlus: Complement Component 4