How is the complement fixation test used in serology?

The complement fixation test (CFT) is a serological test used to detect the presence of specific antibodies or antigens in a patient’s serum. Here’s how it’s used:

1. Principle: The test is based on the ability of antibodies to fix complement, a group of proteins that help eliminate pathogens.

2. Procedure:

a. Patient serum is mixed with a known antigen.
b. Complement is added.
c. If antibodies are present, they bind to the antigen and fix the complement.
d. The mixture is then added to sensitized red blood cells (RBCs).
e. If complement is fixed, the RBCs will not lyse (burst).