Toxoplasma IgM (Toxoplasma Antibody)

What is Toxoplasma IgM?

Toxoplasma IgM is the type of antibody the body produces in the first weeks after encountering the toxoplasma parasite. Although it is generally regarded as a sign of a new infection, in some people it can remain in the blood at low levels for months, or even for more than a year. For this reason, on its own it does not show with certainty when the infection occurred. Tracking how the IgM level changes over time provides much more information than a single measurement.

In healthy adults, toxoplasma infection mostly goes unnoticed or passes with mild fatigue and swollen lymph nodes. However, because an infection acquired for the first time during pregnancy can pass to the baby, the IgM result must be interpreted carefully during this period. The likelihood of transmission to the baby and the possible effects depend on the stage of pregnancy at which the infection occurs. The antibody level is determined in serum using the ELISA technique, and the report is given as negative, gray zone or positive.

When is the Toxoplasma IgM test ordered?

Toxoplasma IgM is ordered when a recent infection is suspected and, together with IgG, in pregnancy screening. When read side by side with the IgG result, it gives a much more reliable picture of the timing of the infection. Because interpretation can be difficult when IgM is ordered alone, doctors usually prefer to run both tests on the same sample. As the IgM response can remain weak in people with weakened immunity, the doctor may use additional methods.

• Screening before and during pregnancy
• A previously negative IgG result turning positive
• Swollen lymph nodes in the neck, fever, muscle pain and fatigue
• Findings suggestive of infection on a pregnancy ultrasound
• Suspected infection in people with weakened immunity

How should I prepare for the Toxoplasma IgM test?

For Toxoplasma IgM you do not need to fast or wait for a particular time of day. Especially in pregnancy, interpreting the result depends largely on timing, so it is important to tell your doctor how many weeks pregnant you are and the results of any toxoplasma tests done before pregnancy. If one of your samples has been tested before, it is recommended to have the next test done at the same laboratory if possible, for comparison.

The blood draw takes a few minutes and usually causes only a brief, mild pricking sensation. You can have every blood draw, including follow-up samples, done at your home or workplace during a visit from a Curavita nurse. After the blood is taken, a small bruise may appear at the puncture site; it usually clears up on its own within a few days.

What does the Toxoplasma IgM result mean?

A negative IgM result suggests that you have not had the infection before if IgG is also negative, and that the infection most likely occurred long ago if IgG is positive. In a very recent exposure antibodies may not yet have formed, so if symptoms persist your doctor may repeat the test. With an IgG-negative, IgM-positive result, the doctor may request a new sample a few weeks later to distinguish a true new infection from a false positive.

A positive result may suggest a recent infection; however, long-persisting IgM or a false positive is also possible. For this reason, the result is clarified with an IgG avidity test, measurements repeated a few weeks apart and, if necessary, confirmatory tests performed at reference laboratories. If an infection is confirmed during pregnancy, monitoring and treatment options aimed at reducing the risk of transmission to the baby are planned by a specialist physician. The cut-off values used for Toxoplasma IgM vary by kit and laboratory, and for most quantitative tests also by age and sex; the reference of the laboratory that runs the test is also stated separately on this page. No decision should be made on the basis of the IgM result alone; the result should be interpreted by a doctor together with symptoms and other tests.