What is C4 complement deficiency?
The complement component 4 (C4) test is a simple blood test that measures the amount of complement C4 circulating in your bloodstream. A low level of C4 is associated with autoimmune diseases, such as lupus and rheumatoid arthritis.
Why does C4 deficiency cause lupus?
The apparent paradox that early complement component (C1q, C2 and C4) deficiencies predispose to lupus has been explained by the beneficial roles of these proteins in promoting the clearance of apoptotic cells and immune complexes (ICs).
Can low C4 be normal?
If only your C4 complement level is low, and all other complement components are normal, it is usually because of an inherited component deficiency. More often, you will have lowered levels of several complement components at once. This is the result of an acquired disease.
Does low C4 mean lupus?
Low complement C4 levels are most commonly found in lupus (systemic lupus erythematosus), an autoimmune disease where the immune system attacks the body’s own tissues [9, 10]. Patients with lupus can have persistently low C4 levels (< 10 mg/dL).
Can C3 and C4 be normal with lupus?
In lupus, both C3 and C4 levels are usually low. If your healthcare provider thinks you may have lupus, you may have other blood tests to see how your immune system is working.
Why is complement low in SLE?
Low complement levels often signify active lupus, especially lupus nephritis. However, it is difficult to ascertain whether low complement levels are due to consumption during inflammation or due to an inherent deficiency of one or more alleles. Even more obfuscating, the two scenarios may exist in one individual.
Why is complement low?
The cause of complement deficiency is genetics (though cases of an acquired nature do exist post infection). The majority of complement deficiencies are inherited as autosomal recessive conditions, while properdin deficiency occurs through X-linked inheritance. MBL deficiency can be inherited by either manner.
How is CVID diagnosis?
The diagnosis of CVID is primarily established by testing for low blood (serum) IgG immunoglobulin concentrations ranging from severely reduced (<100 mg/dL) to just below adult normal range (500-1200 mg/dL). In addition, laboratory testing may reveal normal or, in some cases, reduced numbers of circulating B cells.
Are there any therapeutic options for complement deficiencies?
Therapeutics specific for complement deficiencies are still in the developmental stage for most components, but in some cases, such as C1-Inh deficiency, there are currently several drugs available.
What is the prevalence of secondary complement deficiency?
Secondary complement deficiencies are relatively common. Any pathologic process that results in activation of the complement cascade or interferes with the synthesis of complement components, such as liver disease, can result in a secondary complement deficiency.
How do complement deficiencies lead to systemic auotimmune disorders?
A variety of pathophysiologic mechanisms exist by which complement deficiencies can lead to the development of systemic auotimmune disorders. The two most attractive relate to the role of the complement system in the processing and clearance of immune complexes and the processing and clearance of apoptotic cells.
What is the prevalence of complement deficiency in systemic lupins (SLE)?
Studies using DNA typing methodologies have found the frequency of homozygous C2 deficiency in whites with SLE to be about 1.7%. 191 These studies provide clear support for the association of complement deficiency states with certain rheumatologic disorders, particularly SLE. 192