Definition These tests evaluate the immune system, whose function is to defend the body against such invaders as bacteria and viruses. The immune system also plays a role in the control of cancer, and is responsible for the phenomena of allergy, hypersensitivity, and rejection problems when organs or tissue are transplanted. One of the ways the immune system protects the body is by producing proteins called antibodies. Antibodies are formed in response to another type of protein called an antigen (anything foreign or different from a natural body protein). Immune complex reactions occur when large numbers of antigen-antibody complexes accumulate in the body. Purpose The purpose of the immune complex test is to demonstrate circulating immune complexes in the blood, to estimate the severity of immune complex disease, and to monitor response to therapy. Precautions Because this test is requested when the physician suspects that a patient's immune system is not functioning properly, special care should be taken during and after blood is drawn. For example, the venipuncture site should be kept clean and dry to avoid any chance of infection. Description Immune complexes are normally not detected in the blood. However, when immune complexes are produced faster than they can be cleared by the system, immune complex disease may occur. Examples of such disorders are drug sensitivity, rheumatoid arthritis, and a disease called systemic lupus erythematosus, or SLE. The method generally used for detecting immune complexes is examination of a tissue obtained by biopsy (removal and examination of tissue sample) and the subsequent use of different staining techniques with specific antibodies. However, since tissue biopsies do not provide information about the level of complexes still in the circulatory system, serum assays obtained from blood samples which indirectly detect circulating immune complexes are useful. However, due to the variability of these complexes, several test methods may be used. Also, as most immune complex assays have not been standardized, more than one test may be required to achieve accurate results. Preparation This test requires a blood sample. It is not necessary for the patient to be in a fasting (nothing to eat or drink) state before the test. Risks Risks for this test are minimal, but may include slight bleeding from the blood-drawing site, fainting or feeling lightheaded after venipuncture, or hematoma (blood accumulating under the puncture site). Normal results Normally, immune complexes are not detected in the blood. Abnormal results The presence of detectable immune complexes in the blood is important in the diagnosis of autoimmune diseases, such as SLE and rheumatoid arthritis. However, for definitive diagnosis, the results of other studies must be considered with the presence of any immune complex. For example, immune complexes are associated with high numbers of a component called antinuclear antibodies in the diagnosis of systemic lupus erythematosus. A different example are the kidneys. Because of their filtering functions, elements in the kidneys called renal glomeruli can be affected by immune complexes. In such cases, renal biopsy is used to provide conclusive evidence for immune complex. Key Terms - Antibody
- A (immunoglobulin) molecule that interacts with a specific antigen. Antibodies provide protection from microscopic invaders like bacteria.
- Antigen
- Any substance that is capable under certain circumstances of producing an immune response either from antibodies or T-cells; bacteria are often antigens.
- Autoimmune disorder
- A disorder caused by a reaction of an individual's immune system against the organs or tissues of the body. Autoimmune processes can have different results: slow destruction of a particular type of cell or tissue, stimulation of an organ into excessive growth, or interference in function.
- Biopsy
- The removal and examination, usually under a microscope, of tissue from the living body. Used for diagnosis.
- Systemic lupus erythematosus
- A chronic disease of the connective tissues in the body; characterized by involvement of the skin, joints, kidneys, and serosal membranes (membranes that form the outer covering of organs in the abdomen or chest).
For Your Information Resources Books - Jacobs, David S., et al. Laboratory Test Handbook. 4th ed. New York: Lexi-Comp Inc., 1996.
Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group
The Essay Author is Janis O. Flores.
This article was updated on 08-14-2006
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