Division (b)

Examination for antibodies

Individual serum samples should be tested for their ability to inhibit Newcastle disease virus haemagglutinating antigen in standard haemagglutination inhibition tests as defined in Chapter 6.

There is some debate as to whether 4 or 8 haemagglutinin units should be used for the HI test. It would appear that either is valid and the choice should be left to the discretion of the national laboratories. However, the antigen used will affect the level at which a serum is considered positive: for 4 HAU a positive serum is any showing a titre of 2⁴ or greater and for 8 HAU a positive serum is any showing a titre of 2³ or greater.