What will occur to the RBCs in a negative complement fixation test?

In the context of a negative complement fixation test, the appropriate outcome for red blood cells (RBCs) is that they will hemolyze. This occurs because, in a negative result, the antigen-antibody complex does not form effectively to activate the complement system. Consequently, there will not be sufficient binding of complement components to neutralize the hemolytic activity against the RBCs.

When the test is performed, if there is no specific antibody present to bind the antigen, the complement remains inactive, and as a result, it does not protect the RBCs from hemolysis. Most typically, free complement is available and leads to lysis of RBCs present in the test mixture, demonstrating that the residual complement is acting on the RBCs. Thus, hemolysis is observed as an indicator of a negative test result.

This outcome reflects the principle behind a negative complement fixation test, where the lack of a specific immune reaction leads to the destruction of RBCs rather than a protective clumping or intact status.