Rubella Avidity Test

 Sample: Serum (0.5 mL)


Status:   CY lab

Units: %

Range:   > 30%   High Avidity (Past Infection)

           20 - 30 %  Mean Avidity (Indeterminate)

               < 20%   Low Avidity (Acute infection)

Remarks: Avidity test is of paramount importance to differentiate acute from past infection specially in cases when IgM is positive, because IgM test may remain positive for months even for a year or more after the acute phase. Avidity is the binding strength of the antibody of patient’s serum to bind with theantigen. Low IgG avidity (< 20%) means that there are a few hydrogen bonds and the infection is acute whereas high IgG avidity (> 30%) means that there are many weak hydrogen bonds and the infection is past (more than 5 months) .  In cases when Avidity lies between 20 - 30% it is mandatory to repeat the test  in duplicate after several days using both samples in the same batch of reactions. 



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