The CH50 method is used as a screening test (for the measurement of total classical complement activity) when assessing the ability of an individual to fight infection.
The measurement of complement CH50 activity is now recommended as part of the diagnostic protocol for Primary Immunodeficiency 1,2 and it can also provide important information for many other disease states such as Systemic Lupus Erythematosus and bacterial infections.3
CH50 measures the lysis of antibody-sensitised sheep erythrocytes after addition of fresh serum. The result is expressed as the reciprocal of the dilution that yields 50% erythrocyte (red blood cell) lysis. In comparison the CH100, or total haemolytic complement, is a measurement of 100% lysis of the red blood cells.
The AH50 (or AH100) is used to detect a deficiency of the alternative complement pathway.