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Test Code C2 C2 Complement, Functional, with Reflex, Serum

Performing Laboratory

Mayo Medical Laboratories in Rochester

Reporting Name

C2 Complement,Functional,w/Reflex,S

Specimen Type

Serum Red


Advisory Information


This test is for assessment of complement C2 and includes assessment of C3 and C4 as reflex testing. Unless a deficiency has already been identified, initial assessment should begin with the total complement assay (COM / Complement, Total, Serum), which is a screen for suspected complement deficiencies and should be performed 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 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.


Reject Due To

Hemolysis

Mild OK; Gross OK

Lipemia

Mild OK; Gross reject

Icterus

Mild OK; Gross OK

Other

Serum gel tube

Specimen Stability Information

Specimen Type Temperature Time
Serum Red Frozen 21 days

Specimen Minimum Volume

0.5 mL

Day(s) and Time(s) Performed

Monday through Saturday; 3 p.m.

Specimen Retention Time

14 days

Analytic Time

Same day/1 day

Reference Values

25-47 U/mL

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
C4 Complement C4, S Yes No
C3 Complement C3, S Yes No
C2AG C2 Complement, Antigen, S No No

Useful For

Investigation of a patient with a low (absent) hemolytic complement (CH50), with reflex testing to C3 and C4, if appropriate

Testing Algorithm

If the C2 result is less than 15 U/mL, then C3, C4, and C2AG will be performed at an additional charge.

Method Name

C2: Automated Liposome Lysis Assay

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

86161

86160 x3 (if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
C2 C2 Complement,Functional,w/Reflex,S In Process

 

Result ID Test Result Name Result LOINC Value
C2FX C2 Complement,Functional,S No LOINC Needed
INT53 Interpretation 69048-7

Clinical Information

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. This activation process results in the formation of the lytic membrane attack complex, as well as the generation of activation peptides that are chemotactic for neutrophils and that bind to immune complexes and complement receptors. The absence of early components (C1, C2, 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 generate lytic activity or to clear immune complexes. 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 in 100 to 1 in 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, atrophoderma, cold urticaria, inflammatory bowel disease, and recurrent infections.

 

The laboratory findings that suggest C2 deficiency include a hemolytic complement (CH50) of nearly zero, with normal values for C3 and C4.

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 (or low) 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.

Cautions

As with all complement assays, proper sample handling is of utmost importance to ensure that the complement system is not activated before clinical testing.

 

Absent (or low) C2 functional levels in the presence of normal C2 antigen levels should be replicated with a new serum specimen to confirm that C2 inactivation has not occurred during shipping.

Clinical Reference

1. 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 879-8922

2. O'Neil KM: Complement deficiency. Clin Rev Allergy Immunol 2000;19:83-108

3. Frank MM: Complement deficiencies. Pediatr Clin North Am 2000;47:1339-1354

4. Agnello V: Complement deficiency states. Medicine 1978;57:1-23

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

Method Description

C2 complement activity is measured by mixing patient serum with a C2-deficient serum. The lytic activity of the serum mixture is tested against sensitized, labeled liposomes. If lysis occurs, the patient serum must be the source of the C2. The target liposomes are a commercial reagent (WAKO total complement CH50) and the assay is performed on a Siemens Advia 1200.(Unpublished Mayo information)