Complement Levels

Table of Contents

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.