The terms toxoplasmosis IgG and IgM frequently appear on blood test reports, especially during pregnancy monitoring. These markers help evaluate a person’s immune status concerning toxoplasmosis. Understanding their meaning is essential for correctly interpreting a report and taking appropriate measures if necessary. This article aims to provide clear and factual information to help you decipher your results.

What do Toxo IgG and IgM mean?

The toxoplasmosis blood test looks for the presence of specific antibodies directed against Toxoplasma gondii, a microscopic parasite. When the body encounters this parasite, the immune system produces two main types of antibodies: immunoglobulins M (IgM) and immunoglobulins G (IgG).

• IgM: These are acute phase antibodies. They appear quickly after an infection, usually within one to two weeks. Their presence in the blood most often indicates a recent or ongoing infection.
• IgG: These are immune memory antibodies. They are produced later but persist throughout life. Their presence indicates a past infection and confers lasting protection (immunity).

A healthcare professional analyzes these two markers together. Their presence, absence, and respective concentrations tell the story of the encounter between the body and the parasite. This information is crucial for pregnant women and immunocompromised individuals.

Why is it important to understand toxoplasmosis serology?

Interpreting Toxo IgG/IgM results is a central element of preventive medicine. Toxoplasmosis infection is common and generally benign in healthy individuals. However, it can have serious consequences in specific contexts.

For a pregnant woman, knowing her status is fundamental. If she is not immune (negative IgG), a primary infection during pregnancy can be transmitted to the fetus and lead to complications. Monthly monitoring is then implemented.

For an immunocompromised person, a past infection (positive IgG) can reactivate. The parasite, dormant in the body, can awaken and cause severe damage, particularly to the brain. Monitoring is therefore necessary in this case. Research even suggests links between chronic infection and certain neurological changes, although this area still requires extensive study.

How to read and understand your test results

On your report, you will find two distinct lines, with reference values that may vary slightly from one laboratory to another.

Presentation of results

• Toxoplasmosis IgG: Often expressed in IU/mL (International Units per milliliter).
• Toxoplasmosis IgM: Often expressed by an index or a qualitative ratio (positive/negative).

Typical thresholds are:

• For IgG:
  • Less than 4 IU/mL: Negative (no immunity).
  • Between 4 and 8 IU/mL: Grey zone or equivocal (to be checked).
  • Greater than 8 IU/mL: Positive (probable immunity).
• For IgM:
  • Index < 0.8: Negative.
  • Index between 0.8 and 1.0: Grey zone.
  • Index > 1.0: Positive.

It is crucial to note that it is the combination of the two results that gives the clinical meaning.

Checklist for initial analysis

1. Identify your IgG status (positive or negative).
2. Then check your IgM status (positive or negative).
3. Note the exact IgG value if positive.
4. Look for any mention of “grey zone” or “equivocal.”
5. Check the collection date to contextualize the results.

This approach will allow you to better communicate with your doctor.

Clinical interpretation of Toxo IgG/IgM results

Here are the four possible scenarios and their significance.

1) IgG negative / IgM negative

• Interpretation: Absence of immunity against toxoplasmosis.
• Meaning: You have never been in contact with the parasite. You are therefore susceptible to contracting the infection (primary infection).
• Course of action: For the general population, no particular measures. For pregnant women, monthly monitoring is mandatory, and strict hygiene rules must be applied to avoid contamination.

2) IgG positive / IgM negative

• Interpretation: Acquired immunity (past infection).
• Meaning: You have been infected in the past (generally more than 4 months ago) and are protected against reinfection. This is the most common case in seropositive individuals.
• Course of action: This status is reassuring, especially for a pregnant woman. No monitoring is necessary in immunocompetent individuals. Vigilance is required in cases of severe immunodeficiency (risk of reactivation).

3) IgG negative / IgM positive

• Interpretation: Possible very recent infection or false positive.
• Meaning: This rare case may indicate an infection less than two weeks old (IgG has not yet had time to appear) or a non-specific reaction (false positive IgM).
• Course of action: A blood test is essential after 2 to 3 weeks to check for the appearance of IgG (seroconversion). Confirmatory tests may be requested.

4) IgG positive / IgM positive

• Interpretation: Probable recent infection.
• Meaning: This profile suggests an infection that probably dates back less than 6 months. However, interpretation is delicate because IgM can persist for several months after infection.
• Course of action: Complementary tests are necessary to date the infection more precisely. The most common is the IgG avidity test. High avidity indicates an older infection (> 4 months), while low avidity suggests a recent infection. This dating is crucial in pregnant women.

Practical advice according to your Toxo IgG/IgM status

1) If you are seronegative (IgG- and IgM-)

• Monitoring: A monthly test is necessary if you are pregnant.
• Prevention:
  • Cook all meat (beef, lamb, pork) thoroughly.
  • Wash fruits and vegetables thoroughly.
  • Wash your hands after handling raw meat or touching soil (gardening).
  • If you have a cat, avoid cleaning its litter box or wear gloves.

2) If you are seropositive with immunity (IgG+ and IgM-)

• Monitoring: No monitoring for toxoplasmosis is necessary, even during pregnancy.
• Prevention: No specific dietary precautions for toxoplasmosis are required. Immunocompromised individuals should remain attentive to the appearance of neurological symptoms.

3) If a recent infection is suspected (IgM+)

• Immediate action: Consult a doctor quickly for specialized management.
• Monitoring: Blood tests and complementary tests (avidity) will be planned.

Frequently Asked Questions about Toxoplasmosis

Can you contract toxoplasmosis multiple times?

No. After an initial infection, acquired immunity (presence of IgG) generally protects for life against reinfection.

Are Toxo IgG/IgM tests completely reliable?

They are very reliable, but like any biological test, a margin of error exists (rare false positives or negatives). This is why critical or equivocal results are always confirmed by complementary tests or a new sample.

How to interpret a “grey zone” in my results?

A result in the grey zone or equivocal means that the value is at the limit of the detection threshold. This does not allow for a conclusion. A new blood test after 2 to 3 weeks is essential to see the evolution and clarify the status.

What is a toxoplasmosis reactivation?

This concerns an already immune person (IgG+) whose immune system is severely weakened (AIDS, transplant, chemotherapy). The dormant parasite can then “awaken” and multiply. This phenomenon is different from a primary infection.

Can you “get rid of” seropositivity to toxoplasmosis?

No. Once infected, the parasite remains in the body as dormant cysts, and IgG antibodies persist for life. There is no treatment to eradicate these cysts.

Additional resources

• To deepen your knowledge, click here.
• To extend your knowledge and decipher other markers, more articles are available here.

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