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Test Code C2AG C2 Complement, Antigen, Serum

Reporting Name

C2 Complement, Antigen, S

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Serum Red

Advisory Information

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

Only orderable as a reflex. For more information see C2 / C2 Complement, Functional, with Reflex, Serum.


Patient Preparation: Fasting preferred but not required

Supplies: Aliquot Tube, 5 mL (T465)

Collection Container/Tube: Red top

Submission Container/Tube: Plastic, 5-mL tube (T465)

Specimen Volume: 1 mL

Collection Instructions:

1. Immediately after drawing the specimen, place the tube on wet ice.

2. Spin down and separate serum from clot.

3. Immediately freeze specimen.

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Red Frozen (preferred) 60 days
  Ambient  7 days
  Refrigerated  7 days

Reference Values

Only orderable as a reflex. For more information see C2 / C2 Complement, Functional, with Reflex, Serum.


1.1-3.0 mg/dL

Day(s) and Time(s) Performed

Friday; 1 p.m.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
C2AG C2 Complement, Antigen, S 4484-2


Result ID Test Result Name Result LOINC Value
84141 C2 Complement, Antigen, S 4484-2

Analytic Time

5 days

Method Name

Only orderable as a reflex. For more information see C2 / C2 Complement, Functional, with Reflex, Serum.


Radial Immunodiffusion

Useful For

Diagnosis of C2 deficiency


Investigation of a patient with a low (absent) hemolytic complement (CH50)

Clinical Information

Complement proteins are components of the innate immune system. There are 3 pathways to complement activation: (1) the classic pathway (which is activated by immune complexes), (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, C2, C4, C3) 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.


Although rare, C2 deficiency is the most common inherited complement deficiency. Homozygous C2 deficiency has an estimated prevalence ranging from 1 in 10,000 to 1 in 40,000 (the prevalence of heterozygotes is 1:100 to 1:50). Half of the homozygous patients are clinically normal. However, discoid lupus erythematosus or systemic lupus erythematosus (SLE) occurs in approximately one-third of patients with homozygous C2 deficiency. Patients with SLE and a C2 deficiency frequently have a normal anti-ds DNA titer. Clinically, many have lupus-like skin lesions and photosensitivity, but immunofluorescence studies may fail to demonstrate immunoglobulin or complement along the epidermal-dermal junction.  Other diseases reported to be associated with C2 deficiency include dermatomyositis, glomerulonephritis, vasculitis, atrophodema, cold urticaria, inflammatory bowel disease, and recurrent infections.


An inherited complement component deficiency will result in an undetectable complement level. In addition, low or undetectable levels of complement may be due to acquired deficiencies or complement consumption (eg, as a consequence of infectious or autoimmune processes).


Absent C2 levels in the presence of normal C3 and C4 values are consistent with a C2 deficiency.


Low C2 levels in the presence of low C3 and C4 values are consistent with a complement-consumptive process.


Low C2 and C4 values in the presence of normal values for C3 is suggestive of C1 esterase inhibitor deficiency.


Although there are no pediatric studies on C2, studies on cord blood indicate levels are approximately half adult levels(1) and in other studies(2,3) levels of C1q, C3, and C4 reach adult values by 2 months of age.

Clinical Reference

1. Sonntag J, Brandenburg U, Polzehl D, et al: Complement System in Healthy Term Newborns: Reference Values in Umbilical Cord Blood. Pediatric and Developmental Pathology, 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 Paediatr Scand, 1987,76:939-943

3. Davis ML, Austin C, Messmer BL, et al: IFCC-Standardized Pediatric Reference Intervals for 10 Serum Proteins Using the Beckman Arry 360 System. Clinical Biochemistry, 1996,29:489-492

4. Gaither TA, Frank MM: Complement. In Clinical Diagnosis and Management by Laboratory Methods. 17th edition. Edited by JB Henry. Philadelphia, PA, WB Saunders Company, 1984, pp. 897-892

5. O’Neil KM: Complement Deficiency. Clinical Reviews in Allergy and Immunology. 2000; 19:83-108

6. Frank MM: Complement Deficiencies. Primary Immune Deficiencies: Presentation, Diagnosis, and Management. Pediatr Clin North Am 2000;47:1339-1354

7. Buckley D, Barnes L: Childhood subacute cutaneous lupus erythematosus associated with homozygous complement 2 deficiency. Pediatr Dermatol 1995;12:327-330