After adding sensitized sheep red blood cells in the complement fixation test, all tubes show hemolysis. What does this indicate?

After adding sensitized sheep red blood cells in the complement fixation test, all tubes show hemolysis. What does this indicate?

• A. The patient serum was not heat inactivated.
• B. The sensitized red blood cells were unstable.
• C. The incubation temperature was too low.
• D. The patient serum lacked antibodies to the antigen in question.

Answer: (D)

In a complement fixation test, the outcome depends on whether the patient’s serum contains antibodies to the tested antigen. If such antibodies are present, they bind the antigen and fix complement, so when the indicator sensitized red blood cells are added, there is no free complement to lyse them, resulting in no hemolysis. If those antibodies are absent, the complement remains free and can cause hemolysis of the sensitized sheep red blood cells after the indicator step. Seeing hemolysis in all tubes means the patient serum did not have antibodies to the antigen, so the complement was not fixed.

In a complement fixation test, the outcome depends on whether the patient’s serum contains antibodies to the tested antigen. If such antibodies are present, they bind the antigen and fix complement, so when the indicator sensitized red blood cells are added, there is no free complement to lyse them, resulting in no hemolysis. If those antibodies are absent, the complement remains free and can cause hemolysis of the sensitized sheep red blood cells after the indicator step. Seeing hemolysis in all tubes means the patient serum did not have antibodies to the antigen, so the complement was not fixed.