Sorted By Test Name - Mayo Medical Laboratories

COM
8167
lectin activation (or mannan-binding protein, MBP) pathway. The total hemolytic complement assay
(CH50, COM/8167 Complement, Total, Serum) is the best screening assay for most complement
abnormalities. It assesses the classical complement pathway including early components that activate the
pathway in response to immune complexes, as well as the late components involved in the membrane
attack complex. The CH50 assay will be abnormal if there are specific hereditary or acquired C1-C9
complement component deficiencies or if there is consumption of complement due to immune (or
autoimmune) complexes. The AH50 assay is a screening test for complement abnormalities in the
alternative pathway. The alternate pathway shares C3 and C5-C9 components, but has unique early
complement components designated factors D, B, and P, as well as regulatory factors H and I. This
pathway is activated by microbial polysaccharides and does not require immune complex formation.
Patients with disseminated infections with pyogenic bacteria in the presence of a normal CH50 may have
an absent AH50 due to hereditary or acquired deficiencies of the alternate pathway. Patients with
deficiencies in the alternate pathway factors (D, B, P, H, and I) or late complement components (C3,
C5-C9) are unusually susceptible to recurrent neisserial meningitis. The use of the CH50 and AH50
assays allow identification of the specific pathway abnormality.
Useful For: Investigation of suspected complement deficiency, in conjunction with COM/8167
Complement, Total, Serum
Interpretation: Absent AH50 in the presence of a normal CH50 suggests an alternate pathway
component deficiency. Normal AH50 in the presence of absent CH50 suggests an early (C1, C2, C4)
classic pathway deficiency. Absent AH50 and CH50 in the presence of a normal C3 and C4 suggests a
late (C5, C6, C7, C8, C9) component deficiency. Low AH50 levels in the presence of low C3 and C4
values are consistent with a complement consumptive process. Absent AH50 and CH50 suggests a late
(C3, C5, C6, C7, C8, C9) component deficiency or complement consumption.
Reference Values:
75-170% normal
Clinical References: 1. Frank MM: Medical intelligence current concepts: complement in the
pathophysiology of human disease. N Engl J Med 1987;316:1525-1530 2. Thurman JM, Holers VM:
Brief reviews: the central role of the alternative complement pathway in human disease. J Immunol
2006;176:1305-1310 3. Frank MM: Complement deficiencies. Pediatr Clin North Am
2000;47(6):1339-54
Complement, Total, 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 (or 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, C3, 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 the peptides that are necessary to clear immune complexes and to attract
neutrophils 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. Patients
with deficiencies of the late complement proteins (C5, C6, C7, C8, and C9) are unable to form the MAC,
and may have increased susceptibility to neisserial infections. Undetectable complement levels are found
in patients with specific component deficiencies. Decreased complement levels are found in infectious
and autoimmune diseases due to fixation and consumption of complement.
Useful For: Detection of individuals with an ongoing immune process First order screening test for
congenital complement deficiencies
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