Test Overview
Clinical Utility
Complement proteins are components of the innate immune system. There are 3 pathways to complement activation: 1) the classic pathway, 2) the alternative (or properdin) pathway, and 3) the lectin activation (mannan-binding protein: MBP) pathway. The classic pathway of the complement system is composed of a series of proteins that are activated in response to the presence of immune complexes. The activation process results in the generation of peptides that are chemotactic for neutrophils and that bind to immune complexes and complement receptors. The end result of the complement activation cascade is the formation of the lytic membrane attack complex (MAC).
The absence of early components (C1-C4) of the complement cascade results in the inability of immune complexes to activate the cascade. Patients with deficiencies of the early complement proteins are unable to clear immune complexes or to generate lytic activity. These patients have increased susceptibility to infections with encapsulated microorganisms. They may also have symptoms that suggest autoimmune disease and complement deficiency may be an etiologic factor in the development of autoimmune disease.
More than 30 cases of C5 deficiency have been reported. Most of these patients have neisserial infections.
Method
Nephelometry
Analytical Platform
Siemens Nephelometer II
Method Description
C5 complement antigen is measured by immunonephelometry. Antiserum to C5 is mixed with patient serum, the light scatter resulting from the antibody interaction with C5 is measured, and the signal is compared to standard concentrations of C5.(Unpublished Mayo information; Instruction manual: Siemens Nephelometer II l Version 3, Siemens, Inc., Newark, DE, 2008)
Result Included
C5 Complement
Aliases/Synonyms
Complement component 5
Specimen
Specimen Type
SerumC5 Complement testing is available as functional or antigen testing.
Non-interfaced clients should specify the Test ID C5AG S or "Antigen" when ordering this test. Not doing so will cause processing delays while ICL ascertains which test you are requesting .
Functional test: C5 Complement Functional, Serum
Containers
Preferred Containers
Red top (no additive)
Acceptable Containers
Gold top (clot activator & gel)
Volume
Sample Volume
1 mL
Minimum Volume
0.5 mL
Patient Preparation
Fasting preferred
Collection & Handling
Handling Information
Centrifuge and separate serum. Store and send cold or frozen.
Stability
| Ambient | Refrigerated | Frozen |
|---|---|---|
| 7 days | 28 days | 60 days |
Rejection Criteria
| Criteria | Specification |
|---|---|
| Lipemia | Gross |
Performance & Interpretation
Turnaround Time
8 days
Results
-
C5 Complement Antigenmg/dL10.6 - 26.3
Comment
Low levels of complement may be due to inherited deficiencies, acquired deficiencies, or due to complement consumption (e.g., as a consequence of infectious or autoimmune processes).
Absent C5 levels in the presence of normal C3 and C4 values are consistent with a C5 deficiency. Absent C5 levels in the presence of low C3 and C4 values suggests complement consumption.
A small number of cases have been described in which the complement protein is present but is non-functional. These rare cases require a functional assay to detect the deficiency.
Referral Location
Out-of-Country
Interface & Setup
HL7 Interface Codes
| Order Code | Result Name | Result Codes | Units |
|---|---|---|---|
| C5AG S | C5 Complement, Antigen, S | 64784 | mg/dL |
Test Version
Last Updated
2025-12-19