2. Complement Fixation ?
Complement: a Biologically labile serum factor
that causes the immune cytolysis i.e. lysis of
antibody coated cells.
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positive.jpg
3. Principle
1. Complement is irreversibly bound (fixed) by certain classes of
antibody-antigen complexes.
The degree of fixation is governed by the relative concentration of
antibody or antigen
2. The lysis of RBC that have been sensibilized with RBC’s antibody is
dependent upon the presence of unbound complement.
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Method & Mechanism
1. A known antigen (cardiolipin/Viral Ag/sheep RBC) is
mixed with inactivated patient’s serum
2. Add a measured amount of complement (Guineapig
serum) in the test system
3. The test system is incubated at 37°C for about 1 hour.
4. After 1 hour an indicator system (sensitized RBC) is
added to the test system and again incubated at 37°C for
30 minutes
5. If Ag and Ab matches, they form Ag-Ab complex and
utilizes complement.
6. Observe the result
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Cytolysis / Hemolysis Results
Hemolysis Observed Negative test
No Hemolysis Positive test
- -
+ +
Observation & Results
1. If hemolysis is observed: it indicates the absence of specific antibody in patient
serum, so that complement has not been used which lysed the sensitized RBC
giving hemolysis.
2. If no hemolysis is observed: it indicates that the patient serum contains antibody
which reacts with Ag to form Ag-Ab complex and then fix complement.
so that no complement is available to hemolyse sensitized RBC.
6. Applications
CFT is used to detect and quantify antibody that
does not agglutinate or precipitate with its
antigen.
CFT can detect antibody at level less than 1
microgram per milliliter.
CFT is also used to detect antigen
CFT is Economical
CFT can be used to screen large numbers of
Limitations
Non specific
Time consuming
Labour intense
