Immunology and Serology

1. Baby Jean L. Marquez
BSMLS 3-Y1-IRR1
Immunology and Serology Laboratory
Compliment Fixation Test
1.Define Complement Fixation Test. (2 points)
 Compliment Fixation Test is a classical laboratory diagnostic test used to diagnose acute
or recent infection because it primarily detects IgM class of antibody. The complement
fixation test consists of two systems – antibody complement systems: (a) an indicator
system and (b) a test system.
2.What are the uses of CFT? (1 point)
 Used to detect the presence of either specific antibody or specific antigen in a patient’s
serum.
 It could detect recent infections.
 A test of choice for diagnosis of FMDV prior to ELISA
3.Discuss the procedure being done in Compliment Fixation Test. (5 points)
The complement in the patient's serum is first destroyed by heating. The serum is then
mixed with appropriate viral antigen and after incubation. When the antigen–antibody complexes
are formed, exogenous complement (usually from fresh guinea pig serum) is added. This
complement then binds to the complexes and having been ‘fixed,’ it is then no longer able to
cause lysis of added indicator red cells. Usually, sheep red cells coated with antisheep red cell
antibodies are used as indicators to measure the presence of any residual complement. And then
observe for results.
4.How will you interpret the results? (2 points)
 If there is no hemolysis and the blood settles at the bottom it is positive. Because
complement is completely consumed in the reaction and there is none left
to bind to the SRBC/anti-SRBC complexes it means that the antibodies specific for the
antigen in the assay is present.
 For negative results, hemolysis occurs because patient's serum does not have antigen
specific antibodies, then immune complex is
not formed and, therefore, complement does not get fixed. Complement is thus free to
bind to the SRBC/anti-SRBC complexes (haemolysin) and
cause lysis of SRBCs.

2. 5.What are the advantages and disadvantages of CFT? (5 points)
For ADVANTAGES
 Ability to screen against a large number of viral and bacterial infections at the
same time.
 Economical
For DISADVANTAGES
 Time consuming and labor intensive
 Often non-specific e.g., cross-reactivity between HSV and VZV
 Time consuming and labor intensive