Toxoplasma Avidity Test
Sample: Serum
Schedule:Weekly
Status:  CY lab
Units: %
Range:  > 30%  High avidity (Past Infection)
          20 - 30 % Mean avidity (Indeterminate)
              < 20%  Low avidity (Acute infection)
Remarks: Toxoplasma (T. gondii) is endemic in cats and is excreted by them with faeces. The cyst forms of the parasite infect the humans without any clinical disease but developing antibodies. In certain cases lymphadenitis appears. More serious is the prenatal infection, mainly during the first trimester of pregnancy, where the disease may cause damage to the foetus and in some cases even abortion.
Toxoplasma IgG Avidity test is of paramount importance to differentiate acute from past infection specially in cases when IgM T. gondii is positive, because IgM test may remain positive 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 the Toxoplasma antigen. 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 Toxoplasma IgG 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.ÂÂ
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