Toxoplasma gondii Antibodies, IgM

Qualitative determination of IgM antibodies to Toxoplasma gondii (T. gondii) to aid in the presumptive diagnosis of acute or recent T. gondii infection, including in pregnant women. It is recommended that IgM testing be performed in conjunction with IgG testing. A positive IgM but negative IgG result should be viewed with suspicion; the patient should be retested two weeks after the first test. If the patient is pregnant and IgG/IgM positive, an IgG avidity test should be performed.

IgG Result

IgM Result

Interpretation

Negative

Negative

No serological evidence of infection with Toxoplasma.

Negative

Equivocal

Possible early acute infection or false-positive IgM reaction. Obtain a new specimen for IgG and IgM testing. If results for the second specimen remain the same, the patient is probably not infected with Toxoplasma.

Negative

Positive

Possible acute infection or false-positive IgM result. Obtain a new specimen for IgG and IgM testing. If results for the second specimen remain the same, the IgM reaction is probably a false-positive.

Equivocal

Negative

Indeterminate. Obtain a new specimen for testing or retest this specimen for IgG in a different assay.

Equivocal

Equivocal

Indeterminate. Obtain a new specimen for both IgG and IgM testing.

Equivocal

Positive

Possible acute infection with Toxoplasma. Obtain a new specimen for IgG and IgM testing. If results for the second specimen remain the same or if the IgG becomes positive, specimens should be sent to a laboratory with expertise in toxoplasmosis for further testing.

Positive

Negative

Infected with Toxoplasma for six months or more.

Positive

Equivocal

Infected with Toxoplasma for probably more than one year or false-positive IgM reaction. Obtain a new specimen for IgM testing. If results with the second specimen remain the same, specimens should be sent to a laboratory with expertise in toxoplasmosis for further testing.

Positive

Positive

Possible recent infection within the last 12 months, or false-positive IgM reaction. Specimens should be sent to a laboratory with expertise in toxoplasmosis for further testing.

Low levels of Toxoplasma IgM may persist for months to years after an initial infection. This test has not been cleared/approved by the FDA for blood/plasma donor screening.

Centers for Disease Control and Prevention. Parasites – Toxoplasmosis (Toxoplasma infection). CDC Web site: https://www.cdc.gov/parasites/toxoplasmosis/index.html. Accessed July 2019.