Complement Assay

Test Description:

The term complement refers to the 20 serum beta-globulin protein enzymes which
are a part of the immune system response to antigen-antibody reactions. The complement
system is necessary for phagocytosis, destruction of foreign bacteria, and
mediation of the overall inflammatory response. Activation of the complement cascade
may occur by way of the classic pathway, in which activation is stimulated by
an antigen-antibody response, or by the alternate pathway, in which polysaccharides,
endotoxins, or immunoglobulins are the stimulating forces. Regardless of the
stimulus, the final product of the complement cascade’s work is a complex protein
capable of destroying the cell membrane of the antigen.

To assess the functioning of the complement system and to determine whether
deficiencies of these proteins are contributing to increased infections or increased
autoimmune activity, two of the components are typically measured. C3 is involved
in both the classic and alternate pathways and composes about 70% of the total
complement protein. C4 is involved in only the classic pathway. Individuals found to
be deficient in C4 have a lowered resistance to infection.
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Normal Values
                           C3: 83–177 mg/dL (0.83–1.77 g/L SI units)
                           C4: 15–45    mg/dL (0.15–0.45 g/L SI units) 
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Possible Meanings of Abnormal Values

C3 Complement

Increased                                         Decreased

Infection                                          Anemia
Inflammatory                                   Acute glomerulonephritis
Malignancy with metastasis            Anorexia nervosa
Necrotizing disorders                      Arthralgias
Rheumatic fever                              Celiac disease
Rheumatoid arthritis                       Chronic active hepatitis
                                                         Chronic liver disease
                                                         Cirrhosis
                                                         Congenital C3 deficiency
                                                         Disseminated intravascular coagulation
                                                         Immune complex disease
                                                         Malnutrition
                                                          Multiple myeloma
                                                         Multiple sclerosis
                                                         Renal transplant rejection
                                                         Septicemia
                                                         Serum sickness
                                                         Subacute bacterial endocarditis
                                                         Systemic lupus erythematosus
                                                         Uremia


C4 Complement

Increased                                           Decreased
Cancer                                                Chronic active hepatitis
Juvenile rheumatoid arthritis              Congenital C4 deficiency
Rheumatoid spondylitis                      Cryoglobulinemia
                                                            Glomerulonephritis
                                                            Hereditary angioedema
                                                            Immune complex disease
                                                            Lupus nephritis
                                                            Renal transplant rejection
                                                            Serum sickness
                                                            Subacute bacterial endocarditis
                                                            Systemic lupus erythematosus
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Contributing Factors to Abnormal Values

• Hemolysis of the sample may alter test results.
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Interventions/Implications

Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• No fasting is required before the test.

Procedure

• A 7-mL blood sample is drawn in a red-top collection tube.
• Gloves are worn throughout the procedure.

Posttest

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
   bleeding.
• Label the specimen and transport it to the laboratory.
• Report abnormal findings to the primary care provider.
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Clinical Alerts         
• Risk of infection at venipuncture site due to possible immunocompromised state.
Teach patient to notify health-care provider if drainage, redness, warmth, edema,
or pain at the site or fever occur.