Rubella Avidity Test
Sample: Serum (0.5 mL)
Schedule:Weekly
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.
