Abstract
Complement system plays a crucial role in innate imunity. Complement deficiencies are often associated with severe infections, usually meningoccocal, pneumococcal or caused by Haemophilus influenzae, or with autoimmune diseases, especially systemic lupus erythematodes.
Inherited complement deficiencies are very rare although their prevalence in population may be underestimated due to lower availability of adequate laboratory testing. Acquired complement deficiencies accompany other underlying diseases and often are caused by increased consumption and only partial.