Toxoplasmosis IgG and IgM are the two antibodies your lab measured to work out whether you have ever met a common parasite called Toxoplasma gondii and, if so, roughly when. If you are pregnant and looking at a positive IgM line right now, take a breath first: a positive IgM does not reliably mean you caught this infection recently. IgM can stay in your blood for a year or more after an old infection, and routine test kits produce false positives fairly often. That single fact changes how most of these results should be read.
In this article you’ll learn what IgG and IgM each measure, how to read all four possible combinations of the two, why a positive IgM so often turns out to be misleading, what testing actually settles the question, and what any of it means in pregnancy or if your immune system is weakened.
What toxoplasmosis is, and what IgG and IgM measure
Toxoplasmosis is an infection caused by Toxoplasma gondii, a microscopic parasite that is genuinely common. Most people who catch it never notice: in healthy adults it usually causes nothing at all, or a mild flu-like spell that passes on its own. The parasite then settles into a dormant state in muscle and brain tissue and stays there quietly, held in check by your immune system, for life.
A blood test cannot see the parasite directly. What it measures instead is your immune response: the antibodies you made. Antibodies are proteins your immune system builds to recognize one specific intruder, and they come in classes. Two of them matter here.
IgM, the first responder
IgM is the antibody class your body produces first, usually within one to two weeks of a new infection. Because it appears early, IgM has long been treated as a marker of recent infection. The problem, and this is the heart of this article, is that IgM does not always leave once the infection is old. Our separate article covers the broader role of Immunoglobuline M.
IgG, the long-term memory
IgG appears later, typically one to three weeks behind IgM, rises over a couple of months, and then stays for life. For toxoplasmosis it also means protection: if you have it, you are very unlikely to catch a fresh infection. Our guide explains Immunoglobuline G.
So the two markers answer different questions. IgG asks whether you have ever met this parasite. IgM tries to ask whether you met it recently, and it is far worse at that job than its reputation suggests. Toxoplasma serology usually sits alongside other infection markers, which we cover in our guide to the serology test.
Reading the four toxoplasmosis IgG and IgM combinations
Neither marker means much alone. The pairing carries the information. Here are the four combinations a report can show. Read the last column as a general map, not as instructions: your clinician decides what happens next.
| IgG | IgM | Wat het doorgaans betekent | Gebruikelijke volgende stap |
|---|---|---|---|
| Positief | Negatief | Past infection, long-standing immunity | Usually nothing further; reassuring in pregnancy |
| Negatief | Negatief | Never infected, not immune | Prevention advice, especially in pregnancy |
| Negatief | Positief | Usually a false positive; occasionally a very early infection | Repeat the test in about two to three weeks |
| Positief | Positief | Ambiguous: could be an old infection or a recent one | IgG avidity testing, usually with reference laboratory confirmation |
IgG positive, IgM negative: a past infection and lasting immunity
This is the most common positive pattern, and it is good news. You caught toxoplasmosis at some point in the past, probably years ago, your immune system dealt with it, and you now carry lasting protection. In pregnancy this combination is generally reassuring, because existing immunity makes a new infection that could reach the baby very unlikely. No monitoring is usually needed. The exception is people whose immune defenses later become severely suppressed.
IgG negative, IgM negative: never infected, and not immune
You have never encountered the parasite. Nothing is wrong: most American adults are in this group. There is no immunity to lose and nothing to treat. What this result does is make prevention worth knowing, especially if you are pregnant or planning to be, because you remain susceptible to a first infection.
IgG negative, IgM positive: usually a false positive
This combination causes the most needless alarm, and it is the one most likely to be wrong. An isolated positive IgM with no IgG is, in the large majority of cases, a false positive: the test reacting to something other than toxoplasmosis. The alternative is a genuinely brand-new infection caught before IgG has had time to appear, which is uncommon. Because both are possible, the answer is not to guess but to repeat the test in about two to three weeks. If IgG appears, the infection was real and recent. If IgG stays negative while IgM remains positive, the first result was a false alarm.
IgG positive, IgM positive: ambiguous, and needs dating
Both markers positive is genuinely ambiguous, and it is not the emergency it looks like. It is compatible with an infection from the last few months, and equally compatible with one from years ago whose IgM simply never faded. On its own, this pairing cannot tell the two apart. Distinguishing them takes a different test, called IgG avidity, and usually confirmation at a specialized laboratory.
Why a positive IgM does not mean a recent infection
If you take one thing from this article, take this. Assuming that positive IgM equals fresh infection is the single most common misreading of toxoplasmosis serology, and it has caused real harm: distress, unnecessary investigations, and historically even pregnancies ended on the strength of a result that was never solid. Two separate problems drive it.
IgM lingers long after the infection is over
Toxoplasma IgM does not switch off neatly when an infection resolves. The CDC notes that Toxoplasma-specific IgM can still be detected as long as 18 months after a newly acquired infection, and some people carry it for years. Someone infected three years ago can still show positive IgM today. The antibody is real; the timing story it appears to tell is not.
Routine test kits produce false positives
The commercial IgM kits used by most hospital and community laboratories are built for screening, not for dating an infection. They flag a number of people who do not have a recent infection. Performance also varies between manufacturers and laboratories, which is why the same blood can produce different answers in different places.
Put those two problems together and you get what US specialists actually see. Among patients referred to the national reference laboratory because their local test showed both IgM and IgG positive, the pattern that looks most worrying, roughly three quarters turned out to have an old, chronic infection rather than a recent one.
What actually settles the question
Three tools, in rough order:
- Repeat testing. A second sample two to three weeks later shows whether anything is moving. Antibodies responding to a genuinely new infection change over that interval; a stale IgM sits still.
- IgG avidity. Avidity measures how tightly your IgG antibodies grip the parasite. Grip strength improves with time, so weakly binding IgG suggests a newer immune response and strongly binding IgG an older one. High avidity is the genuinely useful result: it establishes that infection happened at least three to five months ago, which in early pregnancy can effectively rule out infection during that pregnancy. Low avidity is less informative than it sounds, because it can persist for months and does not by itself prove a recent infection.
- Reference laboratory confirmation. Because acute toxoplasmosis is inherently difficult to diagnose, the CDC advises clinicians to seek confirmatory testing through the specialized reference laboratory at Sutter Health in Palo Alto, California, which serves this role nationally. This is standard practice in the US for a suspected acute result, not an extreme measure.
None of this is something you arrange yourself; your clinician orders it. But knowing the pathway exists helps while you wait.
What toxoplasmosis IgG and IgM results mean in pregnancy
Two pieces of context help here, and both are usually missing from what people find online.
The first is that the United States does not screen every pregnancy for toxoplasmosis. Unlike France, which has tested susceptible pregnant women monthly since the early 1990s, US practice is to test selectively, usually because an ultrasound finding raises a question or because there is a specific exposure or symptom worth investigating. This matters for reading your result: if you were tested in the US, you were probably tested for a reason, and it is worth asking your clinician what that reason was. It also means much of the alarming material online was written for a screening system that works differently from yours.
The second is that sequence matters more than any single result. Someone who already had IgG before conceiving is protected. Risk to a baby comes specifically from a first infection acquired during pregnancy or shortly before, which is exactly why dating an infection, rather than simply detecting antibodies, is the whole game. Congenital toxoplasmosis is uncommon in the US, a first infection does not always pass to the baby, and outcomes are better when the situation is identified and managed early.
If your result is unclear, the right next step is a conversation with your obstetrician, who may bring in a maternal-fetal medicine specialist. They can order avidity testing, send samples for reference confirmation, and arrange ultrasound follow-up. Decisions about your pregnancy belong to you and your medical team, with a confirmed result in hand, and never to a single ambiguous IgM on a screen. If you want to know what else is checked routinely, we cover bloedonderzoek tijdens de zwangerschap.
If you are not immune, here is what actually prevents infection
An IgG negative result simply means you are susceptible. Prevention is practical, and it is worth being clear about where the real risk sits, because the popular version of this advice is both inaccurate and unkind.
Food is the bigger route
- Cook meat properly. CDC guidance is whole cuts to 145°F, ground meat to 160°F, and poultry to 165°F. Freezing meat for several days at 0°F also kills the parasite.
- Rinse fruits and vegetables before eating them, particularly anything grown close to the soil.
- Skip raw or undercooked shellfish and unpasteurized goat’s milk.
- Wash your hands, cutting boards, and knives after handling raw meat.
Soil, gardening, and sandboxes
The parasite survives in soil. Wear gloves for gardening or any work with soil or sand, wash your hands afterward, and keep sandboxes covered.
About your cat: no, you do not have to rehome them
Cats are part of the parasite’s life cycle, which is how they acquired a reputation they mostly do not deserve. A cat only sheds the parasite for a short window after catching it themselves, typically by hunting or eating raw meat. ACOG puts it plainly: an indoor cat who eats cat food and does not hunt poses a very low risk. The parasite in cat feces also is not infectious for the first one to five days, so changing the litter box daily removes most of what remains. If you are pregnant and not immune, the simplest arrangement is to have someone else empty the box; if that is not possible, gloves and handwashing do the job. Owning a cat is not something to feel guilty about. Undercooked meat and unwashed produce deserve more of your attention.
Toxoplasmosis when your immune system is weakened
Here the reading of a positive IgG changes. For most people, IgG positive means protected and done. For someone whose immune defenses are seriously suppressed, through advanced HIV, an organ or stem cell transplant, certain cancer treatments, or long-term immunosuppressant drugs, that dormant parasite is held down by an immune system that may no longer manage it. It can reactivate, most importantly in the brain.
This is why toxoplasmosis IgG status is checked before transplants and in people with advanced HIV. Knowing whether the parasite is present at all changes what a care team watches for and which preventive steps they consider. We explain the related testing in our article on HIV-screening, and immune cell counts are covered in our guide to lymfocyten.
Reactivation is a different event from a first infection. If you are healthy and IgG positive, this section is not about you.
Wanneer moet je een arts raadplegen?
Contact your doctor promptly if:
- You are pregnant and any toxoplasmosis result is positive or unclear. Ask for interpretation before drawing conclusions.
- Your IgM is positive and nobody has told you what the next test is.
- You are pregnant, IgG negative, and think you have had a possible exposure.
- You have a weakened immune system and develop persistent headache, confusion, seizures, one-sided weakness, or vision changes. This warrants urgent attention.
- You have swollen glands, fever, or eye symptoms such as blurred vision, floaters, or eye pain that do not settle.
- You are planning a pregnancy and would like to know your immune status in advance.
A note on urgency: an ambiguous IgM in pregnancy deserves a prompt appointment, not an emergency room visit. A genuine acute infection does need timely specialist care, which is precisely why having the result interpreted without delay matters.
Latest scientific advances in toxoplasmosis testing
Recent research keeps landing on the same conclusion: IgM alone cannot date an infection, and avidity testing is what makes serology trustworthy.
A 2025 systematic review and meta-analysis in BMC Pregnancy and Childbirth (a study that pools results from many earlier studies into one larger analysis) gathered 67 studies of toxoplasma antibody testing in pregnancy. What was found: among pregnant women with a positive IgM, only about three in ten showed the low IgG avidity that would point toward a recent infection. What this means for you: a positive IgM in pregnancy far more often reflects an old infection than a new one, and avidity is the test that separates them.
A 2024 retrospective two-center study in the Australian and New Zealand Journal of Obstetrics and Gynaecology (retrospective means researchers looked back through records of patients already seen) reviewed 718 pregnancies tested with TORCH panels, the group of tests that includes toxoplasma. What was found: 15 women had a positive toxoplasma IgM, yet only one had an actual acute infection. What this means for you: real-world confirmation of how often a positive IgM is not a recent infection.
A 2024 narrative review in the Iranian Journal of Parasitology (an expert summary of where the evidence currently stands) mapped the diagnostic toolkit for pregnancy. What was found: when fetal infection genuinely needs confirming, testing amniotic fluid by PCR, a method that looks for the parasite’s DNA directly rather than measuring your antibody response, remains the reference standard. What this means for you: antibodies are the starting point, not the final word.
A 2026 overview in Expert Review of Anti-infective Therapy examined how countries approach congenital toxoplasmosis. What was found: strategies remain strikingly heterogeneous worldwide, ranging from intensive prenatal screening to no systematic testing at all. What this means for you: advice you read online may have been written for a country with a very different system from yours.
None of this changes the core message. An ambiguous result needs interpretation by your medical team, with the right confirmatory testing, before it means anything at all.
Glossarium
| Termijn | Definitie |
|---|---|
| Toxoplasma gondii | The microscopic parasite that causes toxoplasmosis. It is common worldwide and usually harmless in people with normal immune function. |
| Antilichaam | A protein made by your immune system to recognize one specific intruder. Antibodies come in classes, including IgM, IgG, and IgA. |
| IgM | The antibody class produced first after an infection. For toxoplasmosis it can persist long after the infection is over, so it is unreliable on its own for dating. |
| IgG | The long-lasting antibody class that reflects immune memory. For toxoplasmosis it generally stays for life and indicates immunity. |
| Serologie | Testing that looks for antibodies in blood rather than for the germ itself, to find out how your immune system has responded. |
| Seroconversie | The moment antibodies first appear in someone who previously had none. Watching for seroconversion on a repeat sample is how a genuinely new infection is confirmed. |
| IgG avidity | A test measuring how tightly IgG antibodies bind the parasite. Binding strengthens over time, so high avidity points to an infection acquired at least three to five months earlier. |
| Vals-positief resultaat | A test result that reads positive when the condition is not present. Toxoplasma IgM tests produce these relatively often. |
| Reference laboratory | A specialized laboratory that performs and interprets complex confirmatory testing that routine labs are not designed to do. |
| Congenital toxoplasmosis | Toxoplasmosis passed from a pregnant person to the baby, which can happen only after a first infection acquired during or shortly before pregnancy. |
Veelgestelde vragen
Does a positive toxoplasmosis IgG mean I am sick?
No. On its own, a positive IgG with a negative IgM means your immune system met this parasite in the past, handled it, and left behind protective memory. It is a record of something that already happened, not a current illness, and it does not need treating. For most people it is the most reassuring result on the report, because it means a new infection is very unlikely. The exception is people whose immune system becomes severely suppressed later, who should make sure their care team knows their IgG status.
I have a cat. Do I need to give them away while I am pregnant?
No, and please do not. ACOG is clear that keeping your cat is fine. The risk comes from cats who go outdoors and hunt, and even then only for a short shedding window. An indoor cat who eats commercial cat food and does not hunt poses a very low risk. Practical steps cover the rest: have someone else change the litter box if you can, or wear gloves and wash your hands; empty it daily, since the parasite is not infectious for the first one to five days. Statistically, your kitchen deserves more caution than your cat does.
Can I catch toxoplasmosis twice?
Essentially no. Once you have IgG antibodies, you are protected against a new infection, and that protection is generally lifelong. This is why an IgG positive, IgM negative result before or during pregnancy is considered reassuring rather than concerning. The separate scenario worth knowing is reactivation, where a dormant parasite in someone with a severely weakened immune system becomes active again. That is not the same as catching it a second time, and it does not occur in people with normal immune function.
My IgG number is high. Does a higher number mean a worse or more recent infection?
No. This is a common and understandable worry. The IgG concentration does not date your infection and does not measure severity. Levels vary considerably between people and between laboratories, and a high number can perfectly well reflect an infection from a decade ago. What dates an infection is avidity testing and, where needed, comparing samples taken a few weeks apart. If a number on your report is troubling you, ask what it is being compared against, since reference ranges differ from lab to lab.
Should I ask for a toxoplasmosis test if I am pregnant in the US?
Routine toxoplasmosis screening is not standard practice in the United States, so most pregnant people here are not tested unless there is a specific reason, such as an ultrasound finding, a symptom, or a known exposure. That is a deliberate policy difference, not an oversight. If you have a particular concern, such as an immune condition or an exposure you are worried about, raise it with your obstetrician and they can decide whether testing would tell you something useful in your situation.
How long will I have to wait for a clear answer, and why can’t they tell me now?
Waiting is genuinely the hardest part. A repeat sample is usually taken two to three weeks after the first, because that gap is what reveals whether your antibodies are changing. Avidity testing and reference laboratory confirmation add further time. The reason nobody will commit to an answer sooner is that a single ambiguous result honestly does not contain one, and giving you a premature answer would risk being wrong in the direction that causes most harm. Ask your care team for a specific timeline; having a date usually helps.
Bronnen
- Centers for Disease Control and Prevention — About Toxoplasmosis
- Centers for Disease Control and Prevention, DPDx — Toxoplasmosis: laboratory diagnosis and serology
- Centers for Disease Control and Prevention — Preventing Toxoplasmosis
- MedlinePlus, US National Library of Medicine — Toxoplasma blood test
- StatPearls, NCBI Bookshelf — Toxoplasmosis
- American College of Obstetricians and Gynecologists — Is it safe to keep a cat during pregnancy?
- Tork M, Sadeghi M, Asgarian-Omran H, et al. — Assessment of simultaneous IgM, IgG avidity, and IgA testing in diagnosis of acute toxoplasmosis in pregnant women: a systematic review and meta-analysis study — BMC Pregnancy and Childbirth, 2025 — https://doi.org/10.1186/s12884-025-07580-6
- Wade CA, Atkinson N, Holmes NE, Hui L — Clinical utility of maternal TORCH screening in fetal growth restriction: a retrospective two-centre study — Australian and New Zealand Journal of Obstetrics and Gynaecology, 2024 — https://doi.org/10.1111/ajo.13802
- Teimouri A, Mahmoudi S, Behkar A, et al. — Current and emerging techniques for diagnosis of toxoplasmosis in pregnancy: a narrative review — Iranian Journal of Parasitology, 2024 — https://doi.org/10.18502/ijpa.v19i4.17159
- Nguyen TG, Garnaud C, Brenier-Pinchart MP, Robert MG — Diagnosis and treatment of congenital toxoplasmosis: an updated overview — Expert Review of Anti-infective Therapy, 2026 — https://doi.org/10.1080/14787210.2026.2673215
- Dhakal R, Gajurel K, Pomares C, Talucod J, Press CJ, Montoya JG — Significance of a positive Toxoplasma immunoglobulin M test result in the United States — Journal of Clinical Microbiology, 2015 — https://doi.org/10.1128/JCM.01663-15
- Peyron F, Mc Leod R, Ajzenberg D, et al. — Congenital toxoplasmosis in France and the United States: one parasite, two diverging approaches — PLoS Neglected Tropical Diseases, 2017 — https://doi.org/10.1371/journal.pntd.0005222
Verder lezen
- Serology test explained: understanding your infectious disease panel
- Blood tests during pregnancy: what is checked and what your results mean
- IgG blood test: what immunoglobulin G levels mean
- IgM bloedtest: wat hoge en lage waarden betekenen
- Hoe lees je de resultaten van je bloedonderzoek: een complete handleiding
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