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Unit Code 9266:
C5 Complement, Antigen, Serum

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Useful For

Diagnosis of C5 deficiency

 

Investigation of a patient with an absent total

complement (CH[50]) level

Clinical Information

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.

Reference Values

7.4-11.7 mg/dL

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 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 #83392

"C5 Complement, Functional, Serum").

Cautions

The total complement assay (#8167 "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.

Clinical Reference

1.   Sonntag J, Brandenburg U, Polzehl D, et al:  Complement systems

      in healthy term newborns: reference values in umbilical cord

      blood. Pediatr Dev Pathol 1998;1:131-135

 

2.   Prellner K, Sjoholm AG, Truedsson L:  Concentrations of C1q,

      factor B, factor D and properdin in healthy children, and the

      age-related presence of circulating C1r-C1s complexes. Acta

      Peidiatr Scand 1987;76:939-943

 

3.   Davis ML, Austin C, Messmer BL, et al:  IFCC-standardization

      pediatric reference intervals for 10 serum proteins using the

      Beckman Array 360 system. Clin Biochem 1996;29,5:489-492

 

4.   Gaither TA, Frank MM:  Complement. In Clinical Diagnosis and

      Management by Laboratory Methods. 17th edition. Edited by JB

      Henry. Philidelphia, WB Saunders Company, 1984, pp 879-892.

 

5.   O'Neil KM:  Complement defiency. Clin Rev Allergy Immunol

      2000;19:83-108

 

6.   Frank MM:  Complement deficiencies. Pediatr Clin North Am

      2000;47(6):1339-1354

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