Table 1.
Serological tests for Toxoplasma gondii infections
| Name of serological test | Advantages | Disadvantages | Special features |
|---|---|---|---|
| Sabin-Feldman dye test (DT) |
Still considered the gold standard test of toxoplasma serology Highly sensitive, specific, and quantitative |
It can only be carried out in reference centers due to the requirement for live tachyzoites, which are amplified in mouse peritoneum or cell culture | The first test developed for the laboratory diagnosis of T. gondii infection |
| Indirect fluorescent assay (IFA) |
More economical and safer to perform than DT, measuring the same antibodies as the DT Test results are easy to evaluate visually IFA has proved to be specific |
The interpretation is subjective and time-consuming Lower sensitivity compared to the DT False-positive results may occur |
The IFA requires the use of a fluorescence microscope |
| Direct agglutination test |
The direct agglutination test needs no special equipment or conjugates A sensitive, specific, and useful assay that shows good correlation with the DT |
Non-specific immunoglobulins interfere with the test * (but they can be removed by treatment with mercaptoethanol and enzymatic treatment) | Measurement of IgG antibodies to Toxoplasma that react with the membrane antigen |
| Differential agglutination test (HS/AC test) | The AC antigen preparation involves stage-specific antigens that are preferentially detected by IgG antibodies formed against Toxoplasma tachyzoites at the early stages of infection | – |
Sera from individuals with acute infection tended to agglutinate both the HS and AC parasite suspensions Higher titers in the HS agglutination test and lower or negative titers in the AC agglutination were found in in cases which acquired infection in the distant past |
| Latex agglutination test and indirect agglutination test (LAT) | Easy to perform and sensitive | Issues with its specificity | The antibody response in acute infections may not be detected for many weeks, showing the predominance of cytoplasmic antigens present in the assays |
| The immunosorbent agglutination assay (ISAGA) |
A highly specific test for the detection of anti-T. gondii IgM, IgA, or IgE antibodies One the most sensitive commercially available Toxoplasma serologic tests |
It requires a high degree of expertise and is not automated |
Used in reference centers, and usually in neonates suspected of having a congenital infection Also applied for the detection of IgE and IgA |
| Enzyme immunoassays (EIA) |
The most common laboratory Toxoplasma diagnostic test [ELISA and the enzyme-linked fluorescent immunoassay (ELFA) are the two most common EIAs] Available as commercial kits and automated platforms Fast and low-cost screening tests Improved to avoid false-positive results |
Poor standardization due to variations in antigen quality and consequent variable results | The use of recombinant antigens reduces the cost and labor required for the production of diagnostic tests |
| IgG avidity test |
Used to discriminate recently acquired infections from those that occurred in the more distant past The presence of high avidity antibodies is a reliable marker of chronic infection Very useful in pregnant women with positive IgG and IgM titers at their first antenatal visit (during the first trimester of pregnancy) |
Further serologic techniques should be applied when low or borderline avidity results are encountered | No universal threshold has been defined above which avidity is confirmed to be high (most laboratories apply their own interpretation according to their requirements) |
| Immunochromatographic tests (ICT) |
Point-of-care testing Cost-effective User-friendly format Fast time results |
Low sensitivity and specificity | Useful as a screening test |
| Western blotting |
Diagnosis congenital infection in newborns A highly sensitive and specific method for the reliable detection of Toxoplasma infection as a confirmatory test |
– | Very useful for the follow-up testing of pregnant women and their infants or for immunodeficient individuals after HIV infection, malignancies, or organ transplantation |