VLD 421: Veterinary Clinical Biochemistry and Laboratory Diagnosis-II (0+1)

INTERPRETATION OF RESULTS

Observation    

• In the wells where antibodies are present there will be Haemagglutination Inhibition.
• The red blood cells will settle as a button.
• In the wells where antibodies are absent, the red blood cells will agglutinate.
• The end point of the titration is the well that shows complete Haemagglutination Inhibition.
• Look at the size of the button as an indication of the degree of haemagglutination inhibition.
• Use the control well as a point of comparison. Be consistent in determining the endpoint.
• Record the pattern observed in each well on a micro well plate.
• Determine the endpoint.This is the point where there is 100 % inhibition of haemagglutination occurs. Record the antibody level for  serum sample. This is expressed as a log base 2.

Acceptance Criteria for serum against NDV Vaccine        

•  < 2³     -  poor                                                                                         
•  2⁴ -2⁶  - optimum titre                                                                               
•  > 2⁶     -  positive

Elution

• The neuraminidase enzyme present in the virus particle will eventually break the bond between the virus and red blood cells.
• This process is called Elution.
• When the elution occurs, red blood cells are no longer agglutinated.
• They roll down the side of V-bottom microwell plates to resemble the negative settling pattern, a tight button.
• Some Newcastle disease virus strains elute more rapidly and the test must be read before this occurs. 
• Usually elution takes longer than 45 minutes. A control well with virus and red blood cells is useful to determine elution time. 

Advantage

• The Haemagglutination Inhibition Test is simple to perform and requires inexpensive equipment and reagents.
• Haemagglutination Inhibition Test is widely used for the diagnosis of viral infections such as Influenza, Newcastle disease and etc.