Which complement pathway does the CH50 test assess?

The CH50 test, or total complement hemolytic activity test, specifically assesses the classical pathway of the complement system. This pathway is primarily activated by antigen-antibody complexes, which leads to a cascade of reactions that results in the lysis of target cells, often measured using standard red blood cells coated with antibodies.

In utilizing the CH50 test, a patient's serum is exposed to a standardized amount of antibody-coated red blood cells. The degree of hemolysis observed indicates the functional capacity of the classical complement pathway. Low CH50 levels can indicate deficiencies or dysfunctions in various complement components that are part of this pathway, such as C1, C2, C3, C4, or C5.

While the alternative pathway and lectin pathway also contribute to complement activity, the CH50 test does not measure their functionality directly. Therefore, it is focused solely on the classical complement pathway, making it a valuable diagnostic tool for conditions that may affect this specific pathway, such as autoimmune diseases and some types of infections.