Radioimmunoassay and immunodiffusion techniques have made it possible to quantify each of the complement components. For clinical purposes, however, only total complement, C3, and C4 are measured. Total complement (CH₅₀), also known as a hemolytic assay, is measured by exposing a sample of human serum to sheep red cells coated with complement-requiring antibody. Results are expressed as CH₅₀ units, reflecting the dilution at which adequate complement exists to lyse one-half of the test cells. C3 and C4 levels are measured individually by radial immunodiffusion. These latter tests take 24 to 36 hours to complete, and results are easily affected by improper handling of the specimen.²⁴

The causes of alterations in C3 and C4 levels are presented in Table 3-5.

Note: Values for total complement, C3, and C4 may vary according to laboratory methods and the reference range established by the laboratory performing the test.

• Failure to transport the sample to the laboratory immediately may alter test results because complement deteriorates rapidly at room temperature.
• Hemolysis of the sample may alter test results.

• Suspected acute inflammatory disorder as generally indicated by elevated total complement levels
• Suspected immune or infectious disorder (e.g., acute glomerulonephritis, systemic lupus erythematosus [SLE], rheumatoid arthritis, hepatitis, subacute bacterial endocarditis, gram-negative sepsis) or both, as indicated by decreased total complement levels
• Support for diagnosing hereditary deficiencies of complement components as indicated by decreased levels of total complement or of specific components such as C3 and C4, or of both (see Table 3-5)
• Support for diagnosing cancer, especially that of the breast, lung, digestive system, cervix, ovary, and bladder, as indicated by increased levels of C3 and C4 (see Table 3-5)
• Monitoring for the progression of malignant disease as indicated by declining complement levels as the disease progresses
• Support for diagnosing a variety of immune and inflammatory disorders as indicated by altered C3 and C4 levels (see Table 3-5)
• Monitoring of progress after various immune and inflammatory disorders as indicated by levels approaching or within the reference ranges

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

A venipuncture is performed and the sample collected in a red-topped tube or other type of blood collection tube, depending on laboratory preference. The sample must be handled gently to avoid hemolysis and transported to the laboratory immediately.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Complications and precautions: Note and report types and deficiencies of complement components and their relation to an inflammatory or infectious disorder.