In vitro test for the quantitative immunological determination of human
complement C4 in human serum and plasma on COBAS INTEGRA
The complement system can be activated via the classical and the
alternative route. Complement factor C4 participates in activation by the
classical route. A decrease in C4 is common, but complete absence is rare.
A lowered concentration or the complete absence of C4 occurs in
immunocomplex diseases, systemic lupus erythematosus (SLE),
autoimmune thyroiditis and juvenile dermatomyositis. The commencement
of SLE in patients with C4‑deficiencies can often be detected at a very early
stage, and the course of the disease is milder than in patients with normal
complement levels. Infections such as bacterial and viral meningitis,
streptococcal and staphylococcal sepsis and pneumonia are associated
with a fall in C4.
Additional differentiation can be obtained by the determination of C4 when
the level of complement factor C3 is low. If in such cases the concentration
of C4 is normal, then an activation of the alternative route is likely. The main
use of C4 determinations is in assessing the course of hypocomplement
As an acute phase protein, C4 is produced to an increased extent during
inflammatory processes. It is elevated in systemic infections, noninfectious
chronic inflammatory conditions (primarily chronic polyarthritis) and
physiological states (pregnancy). The elevation rarely exceeds twice the
normal value and can mask a reduction in the current consumption.
A variety of methods, such as nephelometry, radial immunodiffusion and
turbidimetry, are available for the determination of complement factor C4.
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