CH50

Sceening test for the diagnosis of complement deficiency. CH50" (CH stands for "hemolytic complement"; the number 50 results from the serum dilution at which 50% hemolysis has occurred) is a laboratory parameter used to determine the activity of the complement system. The CH50 test maps the functional activities of the classical (CH50) activation pathway (see also the AP50 test procedure which maps the functions of the alternative activation pathway.

Patient serum provides the complement source and sheep erythrocytes are the indicator system. Human serum serves as the control (normal), and inactivated patient serum (inactivation at 56 C for 30 min) serves as the blank.

The CH50 test and the (similarly designed) AP50 test are suitable for screening. Both tell approximately the same amount about the terminal lytic portion C5b-9 of the complement cascade. If the CH50 is pathological and the AP50 is normal, a component of classical activation (C1, C4, C2) is decreased or absent. If AP50 is pathological and CH50 is normal, factors of alternative activation (D, B, P) are decreased or absent.

The complement system consists of a system of plasma proteins that can be activated on the surfaces of microorganisms. It was originally discovered as a complementary part of the antibody response (see below acquired immunity). However, it is also involved in the response pathways of innate immunity. The complement system consists of > 30 complement proteins, some with inducible enzymatic activity, as well as receptor proteins and regulatory proteins. They are present in the blood plasma dissolved or cell-bound. These proteins are designated with C and atomic number (e.g. C1; C2 etc.).

C3 is a central component of the complement system and is produced by resident tissue cells such as keratinocytes. The individual complement factors serve, among other things, to defend against microorganisms (e.g. bacteria, fungi, parasites; see also immunodeficiencies primary (complement defects).

Constant amounts of antibody-loaded sheep erythrocytes are incubated with the serum to be tested in geometric dilution. Due to the activation of C3 convertase, the terminal lytic complex hemolyzes the sheep erythrocytes. The preparations are then centrifuged and the degree of hemolysis is determined by photometric determination of hemoglobin in the supernatant. The unit is defined as method-dependent.

Decreased titers

• Consumption of complement factors (physiological for defense against infections, also in autoimmune diseases such as SLE or glomerulonephritis)
• decreased production of complement factors, e.g. liver synthesis damage
• congenital deficiency of complement factors
• Technical errors during sample collection

Increased titers

• Inflammatory diseases (acute phase reaction)

1. https://www.labor-und-diagnose-2020.de/