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Test Code C2FXN C2 Complement, Functional, Serum

Performing Laboratory

Mayo Medical Laboratories in Rochester

Reporting Name

C2 Complement, Functional, S, NR

Specimen Type

Serum Red


Specimen Required


Collection Container/Tube: Red top

Submission Container/Tube: Plastic vial

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.

Additional Information: Fasting preferred.


Reject Due To

Hemolysis

Mild OK; Gross OK

Lipemia

Mild OK; Gross reject

Icterus

Mild OK; Gross OK

Other

NA

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

Useful For

The investigation of a patient with a low (absent) hemolytic complement (CH50)

Method Name

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

LOINC Code Information

Test ID Test Order Name Order LOINC Value
C2FXN C2 Complement, Functional, S, NR 33408-6

 

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.

 

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, atrophodema, 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

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

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.

 

If requested not to reflex low C2 result specimens for C3 and C4 testing, the following comment will be reported; "C2 result is decreased. This could be a result of an inherited C2 deficiency, complement consumption, or C1 esterase inhibitor or deficiency. Analysis of C3 and C4 would be required for further interpretation."

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 879-892

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

3. 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 Hitachi 911. If an abnormally low C2 result is obtained, the laboratory will confirm the deficiency with a quantitative C2 antigen assay (radial immunodiffusion) and also measure C3 and C4 levels to help interpret the abnormal C2 result.(Unpublished Mayo information)