What is the Complement System:
The complement system is a set of blood proteins
that are circulating, acting as mediators of the body's
inflammatory response. They act especially in the
destruction of viruses and bacteria. The complement system
does not require previous exposure to a microorganism like
antibodies do. It also does not keep a memory of
encounters the way antibodies do. Antibodies also need
time to be generated, the complement system does not. For
these reasons the complement system is a very important part of
the immune system and imbalances can adversely affect the
integrity and function of the immune system.
Why it is done:
This test is done to monitor the level of
activity in Lupus as well as to aid in Lupus diagnosis.
How it is done:
This test requires a blood sample to be taken
usually from the arm.
What the test measures:
C3 and C4 are the most commonly measured
complement compounds. CH50 and CH100 (total complement
activity) will be measured if your doctor suspects deficiency
that is not measured by C3 or C4.
How the test is used to monitor Lupus activity:
Since the complement system is used by the body
to help clear immune complexes from the blood, it can be used to
monitor activity in Lupus, particularly with glomerulonephritis
and vasculitis.
Normal Levels:
(normal values may vary from lab to
lab)
Normal levels vary based on a number of factors
including gender, age, and the lab doing the testing. Here
is a basic guideline:
C3 - males: 88 to
252 mg/dl (880 to 2520 mg/L)
females: 88 to 206 mg/dl (880 to 2060
mg/L)
C4 - males:
12 to 72 mg/dl (120 to 720 mg/L)
females: 13 to 75 mg/dl (130 to 750
mg/L)
What
Low levels mean:
Low
complement levels in Lupus usually mean increased disease
activity. When the body uses the complement system to
clear immune complexes from the blood it results in low
complement levels. The complement proteins are not
produced as quickly as they are being used.
