Toxoplasma gondii IgG serology - serum specimen
- LIS Mnemonic: STOX
Collect
Gold (SST - Clot activator & gel)
Volume Required
2 ml whole blood
Minimum Required
1 ml serum
Transport
Room temperature
Stability
N/A
Processing
If multiple viral serologies are being requested from the same specimen, the general rule is to collect a total of 2-4 ml of blood for every 2-3 tests ordered. A single serum specimen is required to determine the immune status of an individual or to test for viral-specific IgM antibodies. Paired sera specimens, collected two to three weeks apart, are required for the diagnosis of a current or recent viral infection when examining specimens for IgG antibody. Obtain the acute phase serum as soon as possible after the onset of illness. The most useful results are obtained by submitting acute and convalescent phase sera together to be tested simultaneously. Evaluation of serum for antibodies to TORCH (Toxoplasma, Rubella, CMV, HSV, etc) agents can be used to detect congenital and perinatal infections in newborns. Two serum specimens should be submitted for testing; one from the mother and the other from her infant. Serological testing is not usually available for body fluids other than serum. However, in patients with viral neurologic disease, cerebrospinal fluid (CSF) may be tested for viral antibody if paired with a serum specimen from the same date.
Days Performed
Tuesday
Reported
Same day
Reflex Testing
N/A
CPT
86777
Methodology
Enzyme Immunoassay
Interpretation
<0.9 - No Toxoplasma gondii IgG antibody detected
0.9-1.10 - Equivocal for Toxoplasma gondii IgG antibody
>1.10 - Positive for Toxoplasma gondii IgG antibody
Reference Values
Negative or no Toxoplasma gondii IgG antibody detected
Remarks
Serological assays provide an indirect diagnostic approach by detecting specific antibody responses to infection. Detection of Toxoplasma gondii-specific IgM in a single serum sample or demonstration of a seroconversion from a negative to a positive IgG antibody response between acute and convalescent sera collected 2-3 weeks apart can be diagnostic of current or recent infection. However, low levels of IgM antibodies may occasionally persist for more than 12 months after infection. Detection of Toxoplasma gondii-specific IgG in a single serum specimen indicates exposure at some time in the past. Negative antibody titers may exclude Toxoplasma gondii infection. Results of serological tests must be interpreted with caution, as measurements of antibody responses to infections can be complicated by numerous factors. NOTE: As suggested by the CDC, any equivocal or positive IgM result for Toxoplasma gondii should be retested using a different assay from another reference laboratory specializing in toxoplasmosis testing (e.g., The Palo Alto Medical Foundation Toxoplasma Testing Laboratory). In pregnant women, a positive IgM test should be followed by an IgG avidity test when it is important to determine the timing of infection. Tests to detect IgA and IgE antibodies are useful for diagnosis of congenital infections and infections in other patients, such as pregnant women. Prenatal testing of amniotic fluid or fetal blood by PCR for Toxoplasma gondii DNA can be diagnostic for congenital toxoplasmosis.
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