14.27 and Mims et. The assay detects antigen-antibody reactions by measuring their effect on complement concentration. Usually one is trying to determine if antibodies are present in a patient's serum - one may also want to determine how much antibody is present and for this the patient's serum would be tested in a series of dilutions. If antibodies are present, complexes will form and complement will be activated. If no antibodies are present, complement will not be activated.
Nothing is visible yet though.
SensSRBC's are sheep RBC's which have been reacted with a limited amount of rabbit anti-SRBC's. If complement was activated by the earlier antigen-antibody reaction then the sensitized SRBC's will remain intact and Complement fixation is positive. Complement fixation is negative. 14.27 shows an example of a CF test for antibodies to Coxiella. Proof that this organism was the one causing the illness.