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Also Known As:  Complement Antigen, C3, C4. CH50, Complement Activity, Complement Assay

What is a Complement Component Test?

The Complement Component  is a blood test that helps measure the activity or amount of specific proteins in the liquid part of your bloodstream. The complement system comprises up to 60 proteins, among which 30 are circulating blood proteins working together to facilitate inflammatory and immune responses in the body. A complement system's primary role is to help specify, decimate, and eliminate foreign pathogens such as viruses, bacteria, and other damaged self-materials like proteins and cells. As the name suggests, the complement system aids in your natural body defense via antibodies. Therefore, it activates when the body makes antibodies against foreign particles or itself.

In general, the complement system is a part of your body's innate immune system. Like the acquired system producing antibodies to protect specific dangers, the natural system is non-specific and instantly responds to foreign materials. There is no need for previous exposure or encounter to invading viruses or bacteria in the body.

As far as primary complement proteins are concerned, there are 9 of them designated C1 till C9. These complement proteins, along with other proteins, work in synergy via cascade-like methods to activate, amplify, break and form several protein complexes against infections, dead cell debris, non-self-tissues, and inflammation. For the complement cascade, there are three Pathways, i.e., classical pathway (c1qrs, C2, C4), alternative pathway (C3, factor B, and properdin), and lectin pathway (MBL, i.e., mannan-binding pathway). The result for all is the same, i.e., the formation of MAC (membrane attack complex).  

This test measures the function or amount of complement proteins in the blood. The complement components can be studied individually or together to understand whether the complement system is functioning correctly. C3 and C4 are frequently measured, but your healthcare practitioner can also opt for total complement activity if they think a deficiency is not accurately measured. The CH50 functional test, on the other hand, benchmarks the function of the complete classical complement pathway intervened through components C1 till C9. If the results are outside normal levels, the doctor can measure each of the nine different components to understand your body's acquired or hereditary deficiencies.

What Is The Test Used For?

A complement blood test is most commonly used for the diagnosis and monitoring of autoimmune disorders like:

Rheumatoid arthritis, a condition that leads to swelling and pain of the joints, especially those present in your hands and feet.

Lupus, a chronic illness that affects multiple organs of your body, including the brain and kidney.

It can also be used to understand whether the abnormalities and deficiencies in the body's complement system are the root cause of your certain medical condition. Total complement activity, i.e., CH50, is used to check the integrity of the classical complement pathway. In most cases, it is limited to:

Diagnosis of the causes of frequent microbial infections, inflammation, or angioedema.
Monitoring and diagnosis of acute or chronic autoimmune disorders such as systemic lupus erythematosus.
Monitoring of the immune-complex-related disorders and conditions, for example, vasculitis, serum sickness, and glomerulonephritis.

Why And When Do You Need The Complement Component Blood Test?

Your doctor will order this test if you are experiencing unexplained edema or inflammation with symptoms related to any autoimmune disorder like lupus. The healthcare professional can also suggest this test if you have an immune complex related condition and wish to know about the body's complement system. They can ask for individual complement components if the total component activity (CH50) is abnormal to know regarding deficient components. Mostly C3 and C4 levels are ordered, but they can check for others as well if they suspect certain deficiencies. After diagnosing an acute or chronic condition, this test can give your doctor a rough idea about the severity of your problems linked to the decrease in complement levels. The symptoms of autoimmune disorder, especially those of lupus, include:

  • Mouth sores
  • Fatigue and tiredness
  • Butterfly shaped rash across your cheeks and nose area
  • Sensitivity to light
  • Extreme hair loss
  • Chest pain during deep breaths
  • Swollen lymph nodes
  • Fever
  • Severe joint pain

What Kind Of Sample Is Required For The CH 50 Blood Tes?

During the Complement Component C3, C4, CH 50 Blood Test, your healthcare professional will take a blood sample, most often through the vein in your arm. You may feel a little tingling or pricking sensation from the needle, but it usually goes away on its own once the needle is out of the puncture site.

Do You Need To Prepare For The Test?

There are no special preparations needed for the complement component test.

Are There Any Risks To This Test?

Even though the blood draw carries little to no risks, some people might experience:

  • Lightheadedness
  • Fainting or dizziness
  • Excessive bleeding
  • Infection at the puncture site when the skin is broken

It is better to notify the doctor right away if you experience any of the above symptoms.

What Do The Test Results Mean? 

Your complement levels may be low due to hereditary deficiency. This hereditary deficiency within the complement proteins can cause a high rate of recurrent microbial infections in the body. These low complement levels are also linked with an increased risk of autoimmune disorders. If this deficiency is because of any underlying acute or chronic condition, the result levels will usually return to normal after resolving the underlying disease. 

Low complement activity can be due to:

  • Immune complex diseases like serum sickness
  • Recurrent microbial infections due to bacteria
  • Shock or septicemia
  • Autoimmune disorders like rheumatoid arthritis and lupus
  • Malnutrition
  • Hepatitis and cirrhosis
  • Acquired or hereditary angioedema
  • Different types of kidney diseases like lupus nephritis, glomerulonephritis, membranous nephritis, and kidney transplant rejection

The Complement Component C3, C4, CH 50 Blood Test results are usually high during acute or chronic inflammation. It can be due to:

  • Juvenile rheumatoid arthritis
  • Certain cancers like leukemia, sarcoma, and Hodgkin lymphoma
  • Sarcoidosis
  • Ulcerative colitis
  • Acute myocardial infarction

Related Tests:   Complement C4a Plasma, Complement C1q Blood Test, Complement C2 Blood Test, C3a Fragment Blood Test, C3 Complement Blood Test

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr.Saad Zia on June 03, 2023.


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