Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

C3
8174
C4
8171
Interpretation: An undetectable C1q in the presence of an absent CH(50) and normal C2, C3, and
C4 suggests a congenital C1 deficiency. A low C1q in combination with a low C1 inhibitor and low C4
suggests an acquired C1 inhibitor deficiency.
Reference Values:
12-22 mg/dL
Clinical References: 1. Frank MM: Complement in the pathophysiology of human disease. N
Engl J Med 1987 June 11;316(24):1525-1530 2. Frank MM: Complement deficiencies. Pediatr Clin
North Am 2000 December;47(6):1339-1354 3. Frigas E: Angioedema with acquired deficiency of the
C1 inhibitor: a constellation of syndromes. Mayo Clin Proc 1989 October;64(10):1269-1275
Complement C3, Serum
Clinical Information: The complement system is an integral part of the immune defenses. The
primary complement pathway consists of recognition (Clq, Clr, Cls), activation (C4, C2, C3), and attack
(C5, C6, C7, C8, C9) mechanisms with respect to their role in antibody-mediated cytolysis. The
complement system can be activated via immune complexes, and the alternative pathway (properdin
pathway), which is activated primarily by foreign bodies such as microorganisms. C3 activation
involves cleavage by C3 convertase into C3a and C3b. When immune complexes are not involved, the
alternate method of complement activation initiates the reactant sequence at C3, bypassing C1, C4, and
C2. Severe recurrent bacterial infections occur in patients with homozygous C3 deficiency and in those
patients with low levels of C3 secondary to the absence of C3b activator. Decreased C3 may be
associated with acute glomerulonephritis, membranoproliferative glomerulonephritis, immune complex
disease, active systemic lupus erythematosus, septic shock, and end-stage liver disease.
Useful For: Assessing disease activity in systemic lupus erythematosus Investigating an undetectable
total complement (CH[50]) level
Interpretation: A decrease in C3 levels to the abnormal range is consistent with disease activation in
systemic lupus erythematosus.
Reference Values:
75-175 mg/dL
Clinical References: 1. Ross SC, Densen P: Complement deficiency states and infection:
epidemiology, pathogenesis, and consequences of neisserial and other infections in an immune
deficiency. Medicine 1984;63:243-273 2. Frank MM: Complement in the pathophysiology of human
disease. N Engl J Med 1987;316:1525-1530
Complement C4, Serum
Clinical Information: The complement system is an integral part of the immune defenses. It can be
activated via immune complexes (classic pathway) or by bacterial polysaccharides (alternative
pathway). The classic complement pathway consists of recognition, (C1q, C1r, C1s), activation (C2, C3,
C4), and attack (C5, C6, C7, C8, C9) mechanisms with respect to their role in antibody-mediated
cytolysis. C4 is 1 of the activation proteins of the classic pathway. In the absence of C4, immune
complexes will not be cleared by C3 activation peptides, but bacterial infections can still be defended
via the alternative pathway. C4 may be decreased in systemic lupus erythematosus, early
glomerulonephritis, immune complex disease, cryoglobulinemia, hereditary angioedema, and congenital
C4 deficiency.
Useful For: Investigating an undetectable total complement (CH[50]) Confirming hereditary
angioedema (with low C1 inhibitor) Assessing disease activity in systemic lupus erythematosus,
proliferative glomerulonephritis, rheumatoid arthritis, and autoimmune hemolytic anemia
Interpretation: Decreased in acquired autoimmune disorders, in active phase of lupus
erythematosus, and in rheumatoid arthritis An undetectable C4 level (with normal C3) suggests a
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