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Complement Blood Test

Last updated July 24, 2019

Approved by: Krish Tangella MD, MBA, FCAP

he Complement Blood Test is a test to assess the levels of complement proteins present in blood. It is used to determine, if deficiencies in the complement system are contributing to an immune disorder.


What are the other Names for this Test? (Equivalent Terms)

  • Complement Activity Blood Test
  • Total Complement Blood Test
  • Total Hemolytic Complement Blood Test

What is Complement Blood Test? (Background Information)

  • Complement is an immune cascade comprising of 11 complement proteins C1 to C10 that circulate in the blood stream. It is part of the body’s innate or non-specific immune response
  • The adaptive immune system is acquired through exposure to specific disease-causing agents, during the course of one’s life. It is made possible by lymphocytes, such as T cells and B cells. B cells form plasma cells, the body’s main antibody-producing factories
  • The body’s innate (or natural) immune system is present at birth. It defends the body from a wide array of offending agents, and does not distinguish between them.  The innate immune system is made up of the following components:
    • Barriers, such as the skin and mucous surfaces - they protect the body against the outside world
    • Phagocytes, such as macrophages - they ingest offending agents
    • Surveillance cells, such as natural killers - they patrol for abnormal cells
    • Inflammation, orchestrated by mast cells - mast cells release chemicals that help isolate an area of damage and initiate repair processes
    • Fever, which elevates body temperatures to speed metabolism and combat infection
    • Complement, formed by the complement proteins C1 through C10: They complement or assist antibodies of the adaptive immune system. They also stimulate inflammation and the action of immune cells
  • The complement system is most often activated, when circulating C1 encounters a cell bound by antibodies. C1 then attaches and acts as an enzyme. It activates other C proteins it encounters, which in turn activates others
  • This cascade of enzymatic activations ends with the formation of the membrane attack complex (MAC). MAC attacks the membrane of the pathogen and kills it. It does this by forming a pore in the membrane, which destabilizes the entire cell
  • The Complement Blood Test is a test to assess the levels of complement proteins present in blood. It is used to determine, if deficiencies in the complement system are contributing to an immune disorder
  • The test can assess levels of individual complement proteins, most often C3 and C4; it can also be used to assess the levels of all complement proteins

What are the Clinical Indications for performing the Complement Blood Test?

Following are the clinical indications for performing the Complement Blood Test:

  • Frequent and persistent infections
  • Chronic inflammation
  • Joint pain or stiffness
  • Chronic fever
  • Fatigue

How is the Specimen Collected for Complement Blood Test?

Following is the specimen collection process for Complement Blood Test:

Sample required: Blood

Process: Insertion of a needle into an arm vein.

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Complement Blood Test Result?

The significance of the Complement Blood Test is explained:

  • Increased levels of complement may indicate:
    • Acute-phase immune response
    • Cancer
    • Ulcerative colitis
    • Heart attack (acute myocardial infarction)
    • Sarcoidosis
  • Decreased levels of complement may indicate:
    • Acquired deficiency
    • Rheumatoid arthritis
    • Vasculitis
    • Severe trauma
    • Systemic lupus erythematosus
    • Membranous glomerulonephritis
    • Cryoglobulinemia
    • Liver disease or cirrhosis

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • The complement is responsible for the destruction of red blood cells, after mixing of incompatible samples

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

References and Information Sources used for the Article:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: June 12, 2014
Last updated: July 24, 2019