Sorted By Test Name - Mayo Medical Laboratories

C2AG
84141
C2FXN
32137
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-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, Philadelphia, WB Saunders Company, 1984; pp 897-892 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
C2 Complement, Antigen, Serum
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. 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. Although
rare, C2 deficiency is the most common inherited complement deficiency. Homozygous C2 deficiency has
an estimated prevalence ranging from 1:10,000 to 1:40,000 (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 erythematousus (SLE) occur in approximately 1/3 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.
Useful For: Diagnosis of C2 deficiency Investigation of a patient with an absent total complement
(CH[50]) level
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
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.
Reference Values:
1.1-3.0 mg/dL
Clinical References: 1. Gaither TA, Frank MM: Complement. In Clinical Diagnosis and
Management by Laboratory Methods. 17th edition. Edited by JB Henry. Philadelphia, WB Saunders
Company, 1984, pp 879-892 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.
Buckley D, Barnes L: Childhood subacute cutaneous lupus erythematosus associated with homozygous
complement 2 deficiency. Pediatr Dermatol 1995;12:327-330
C2 Complement, Functional, Serum
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
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