C7 Complement, Functional, Serum

CPT CODE:

  • 86161

USEFUL FOR:

Diagnosis of C7 deficiency
Investigation of a patient with an undetectable total complement (CH[50]) level

SPECIMEN REQUIRED:

Draw blood in a plain, red-top tube(s) or a serum gel tube(s) froma fasting patient. Spin down, separate from clot, and send 1 mL of serum frozen in plastic vial.

TRANSPORT TEMPERATURE:

Frozen\Refrig NO\Ambient NO

CLINICAL INFORMATION:

Complement proteins are components of the innate immune system. There are 3 pathways to complement activation: 1) theclassic pathway, 2) the alternative (or properdin) pathway, and3) the lectin activation (mannan-binding protein,[MBP]) pathway.The classic pathway of the complement system is composed ofa series of proteins that are activated in response to the presenceof immune complexes. The activation process results in thegeneration of peptides that are chemotactic for neutrophils andthat bind to immune complexes and complement receptors. Theend result of the complement activation cascade is the formationof the lytic membrane attack complex (MAC).
Patients with deficiencies of the late complement proteins (C5,C6, C7, C8, and C9) are unable to form the MAC, and may have increased susceptibility to neisserial infections.
The majority of cases of C7 deficiency have neisserial infections, but cases of systemic lupus erythematosus (SLE), rheumatoidarthritis (RA), scleroderma, and Pyoderma gangrenosum havebeen reported. The pathogenesis of the rheumatic disease is notclear.
Complement levels can be detected by antigen assays that quantitate the amount of the protein (#84142 "C7 Complement, Antigen, Serum"). For most of the complement proteins, a small number of cases have been described in which the protein is present but is non-functional. These rare cases require a functional assay to detect the deficiency.

CLINICAL INTERPRETATION:

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 C7 levels in the presence of normal C3 and C4 values are consistent with a C7 deficiency. Absent C7 levels in the presenceof low C3 and C4 values suggest complement consumption.

REFERENCE VALUES:

36-60 unit/mL