In which type of disorders would you expect decreased levels of C3, C4, and CH50?

Decreased levels of C3, C4, and CH50 are often indicative of the complement system's consumption due to ongoing immune complex formation and inflammation typically seen in autoimmune disorders such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). In these conditions, the body produces antibodies against its own tissues, leading to the formation of immune complexes that activate the complement pathway. This activation results in the consumption of complement proteins, including C3 and C4, as they are used up in the process of mediating immune responses and clearing these complexes. CH50 reflects the total hemolytic activity of the complement system and is similarly affected in these autoimmune conditions.

In contrast, while immunodeficiency disorders may lead to complications affecting complement levels, they primarily involve a deficiency in antibody production or function rather than direct consumption of complement components. Tumors may influence immune function but do not typically lead to the consumption pattern seen in autoimmune disorders. Lastly, infections can affect complement levels, but they often do not show a consistent decrease in all components like C3, C4, and CH50 simultaneously in the same way as seen in autoimmune diseases.