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HelpTest Code C5AG C5 Complement, Antigen, Serum
Reporting Name
C5 Complement, Antigen, SUseful For
Diagnosis of C5 deficiency
Investigation of a patient with an absent total complement (CH50) level
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
SerumOrdering Guidance
The total complement assay (COM / Complement, Total, Serum) should be used as a screen for suspected complement deficiencies before ordering individual complement component assays. A deficiency of an individual component of the complement cascade will result in an undetectable total complement level.
Specimen Required
Patient Preparation:
Fasting: 12 hours, preferred but not required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL Serum
Collection Instructions: Centrifuge and aliquot serum into a plastic vial.
Specimen Minimum Volume
Serum: 0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Frozen (preferred) | 60 days |
| Refrigerated | 28 days | |
| Ambient | 7 days |
Reference Values
10.6-26.3 mg/dL
Day(s) Performed
Tuesday, Friday
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
86160
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| C5AG | C5 Complement, Antigen, S | 4505-4 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| C5AG | C5 Complement, Antigen, S | 4505-4 |
Clinical Information
Complement proteins are components of the innate immune system. There are 3 pathways to complement activation: the classic pathway, the alternative (or properdin) pathway, and 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). More than 30 cases of C5 deficiency have been reported. Most of these patients have neisserial infections.
The C5 antigen test measures the concentration of C5 and is used to study complement component 5 deficiency. If a patient is being treated with eculizumab or another C5 inhibitor, the concentration of C5 may be elevated, as the reagents in this immunoassay cannot distinguish between free C5 and C5 bound to a C5 inhibitor. Testing for alternative pathway function or specifically for C5 function will provide more insight into whether the C5 is free, particularly if the goal of testing is therapeutic drug monitoring for a C5 inhibitor.
Interpretation
Low levels of complement may be due to inherited deficiencies, acquired deficiencies, or due to complement consumption (eg, 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 suggest complement consumption.
A small number of cases have been described in which the complement protein is present but is nonfunctional. These rare cases require a functional assay to detect the deficiency; for more information see C5FX / C5 Complement, Functional, Serum.
Method Description
In this Siemens Nephelometer II method, the light scattered onto the antigen-antibody complexes is measured. The intensity of the measured scattered light is proportional to the amount of antigen-antibody complexes in the sample under certain conditions. If the antibody volume is kept constant, the signal behaves proportionally to the antigen volume.
A reference curve is generated by a standard with a known antigen content on which the scattered light signals of the samples can be evaluated and calculated as an antigen concentration. Antigen-antibody complexes are formed when a sample containing antigen and the corresponding antiserum are put into a cuvette. A light beam is generated with a light-emitting diode, which is transmitted through the cuvette. The light is scattered onto the immuno-complexes that are present. Antigen and antibody are mixed in the initial measurement, but no complex is formed yet. An antigen-antibody complex is formed in the final measurement.
The result is calculated by subtracting value of the final measurement from the initial measurement. The distribution of intensity of the scattered light depends on the ratio of the particle size of the antigen-antibody complexes to the radiated wavelength.(Instruction manual: Siemens Nephelometer II Operations. Siemens, Inc; Version 2.4, 07/2019; Addendum to the Instruction Manual 2.3, 08/2017)
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | Reject |
| Gross icterus | OK |
Method Name
Nephelometry