The complement C4 test is one of the most frequently used complement component tests. Your doctor may order a complement C4 test if you’re experiencing symptoms that indicate an autoimmune disease. These symptoms may include:
- extreme fatigue
- muscle pain
- joint pain
- sudden, unexpected weight loss
- muscle weakness
- muscle paralysis
The complement C4 test is also sometimes used to monitor protein levels in people who have already been diagnosed with an autoimmune disease. Complement tests can provide doctors with valuable information about the effectiveness of current treatment for an autoimmune condition.
These proteins are part of your complement system, an important part of your immune system that helps kill disease-causing bacteria and viruses.
Lower-than-normal complement C4 values could indicate:
- bacterial infections
- hepatitis
- malnutrition
- rejection of a kidney transplant
- systemic lupus erythematosus, which is an autoimmune disease affecting the skin, joints, kidneys, and other organs
- lupus nephritis, which is a kidney disorder that often occurs as a result of systemic lupus erythematosus
- cirrhosis, which indicates significant liver damage
- glomerulonephritis, which is a type of kidney disease
- hereditary angioedema, which is a rare but serious autoimmune disease that causes swelling in various parts of the body
- Complement component activity varies throughout the body. People with rheumatoid arthritis, for example, may have high complement levels in their blood but low complement levels in their joint fluid.
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If your results show higher than normal amounts or increased activity of complement proteins, it may mean you have one of the following conditions:
- Certain types of cancer, such as leukemia or non-Hodgkin lymphoma.
- Levels will be increased in patients with autoimmune hemolytic anemia.
- Ulcerative colitis, a condition in which the lining of the large intestine and rectum become inflamed.
- If you are being treated for lupus or another autoimmune disease, increased amounts or activity of complement proteins may mean your treatment is working.
Note: Your complement levels will often shoot up dramatically just after an infection or injury.
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