In the complement fixation test, what result is expected from a positive control?

In the complement fixation test, a positive control is used to ensure that the test reagents and conditions are working properly. A positive control typically demonstrates the expected outcome of the test when specific antibodies are present. In this context, the expected result for a positive control is no hemolysis, indicating that complement has been fixed by antibodies present in the serum sample being tested.

This absence of hemolysis occurs because the complement has been activated and bound to the antigen-antibody complex, leading to a scenario where the complement system is consumed in the process and unable to lyse the red blood cells that are also part of the test. Thus, the lack of hemolysis confirms that the assay is functioning correctly and that the test will yield valid results.

The other options represent various states of hemolysis, which would not be expected in a positive control scenario. If hemolysis occurred, it would indicate that the complement system was not effectively fixed, which would call into question the reliability of the results and would signify a problem with the test conditions or reagents used in the assay.