A toxoplasmosis test is a blood test that checks for antibodies to the Toxoplasma gondii parasite. Your body's natural defence system (immune system) will make these antibodies only if you have been infected by this tiny parasite. The amount and type of antibodies you have shows whether your infection is recent or occurred in the past. More than one blood test may be done over several weeks.
For most people, toxoplasmosis is not dangerous and goes away on its own. But if a pregnant woman becomes infected and passes it on to her growing baby (fetus), it can cause blindness and brain damage in the fetus.
You can become infected by eating food such as undercooked or raw meat from an infected animal or by handling an infected cat or its stool (feces). After you have been infected, you will have antibodies to Toxoplasma gondii for the rest of your life, so you cannot be infected again.
Why It Is Done
A toxoplasmosis test is done to check if a:
- Pregnant woman has antibodies from a toxoplasmosis infection. If she has the IgG type of antibody, that means an infection occurred in the past and the baby does not have a chance of becoming infected. If she has the IgM type of antibody, that means the infection is recent and the baby does have a chance of becoming infected.
- Baby has toxoplasmosis.
- Person with a weakened immune system, such as someone who has HIV, has a chance of getting a toxoplasmosis infection.
How To Prepare
Tell your doctor if you are pregnant and have contact with a cat or clean a cat's litter box. Before your blood is drawn, let your doctor know if you have bleeding or clotting problems, or if you take blood-thinning medicine.
You do not need to do anything else before you have this test.
How It Is Done
The health professional taking a sample of your blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Apply a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure on the site and then put on a bandage.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of problems from having blood drawn from a vein. You may get a small bruise at the site. You can lower your chance of bruising by keeping pressure on the site for several minutes.
In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. You can use a warm compress several times a day to treat this.
A toxoplasmosis test is a blood test that checks for antibodies to the Toxoplasma gondii parasite. The results of the test are usually given in titres. A titre is a measure of how much the blood sample can be diluted with a saltwater solution (saline) before the antibodies can no longer be found. Test results are usually ready in 1 to 3 days.
A titre of 1 to 8 (1:8) means that antibodies can be found when 1 part of the blood sample is diluted by up to 8 parts of a saltwater solution (saline). A larger second number means there are more antibodies in the blood. So a titre of 1 to 128 means there are more toxoplasmosis antibodies in the blood than a titre of 1 to 32.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range that your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
IgM in babies:
IgM in adults:
Less than 1:64
Less than 1:1024
Toxoplasmosis antibodies usually form within 2 weeks after being infected. The titre is the highest 1 to 2 months after infection.
- If high titres of the IgM type of antibody are found, it means the infection is recent. If high titres of the IgG type of antibody are present, it means an infection occurred in the past.
- Blood samples may be taken over several weeks to see if the number of antibodies is getting higher. This would mean the infection is recent.
- Low titres that do not get higher usually mean the infection occurred in the past. After you have had toxoplasmosis, you cannot be infected again.
What Affects the Test
Other infections can cause a false-positive result in a newborn.
Other antibodies, such as rheumatoid factor or antinuclear antibodies, may also cause a false-positive result.
What To Think About
- If your baby has the IgG antibody, he or she is not infected. If your baby has the IgM antibody, he or she does have toxoplasmosis.
- Your newborn baby may be given a TORCH test at the same time as a toxoplasmosis test. TORCH stands for T oxoplasmosis, O ther, R ubella, C ytomegalovirus, and H erpes. The TORCH test checks to see if your baby has any of these infections.
- The toxoplasmosis polymerase chain reaction (PCR) test checks your amniotic fluid to see if toxoplasmosis is present. This test may be more accurate than other tests in finding an infection in your growing baby (fetus).
To learn more about toxoplasmosis infection in pregnancy, see the topic Toxoplasmosis During Pregnancy.
- Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.
Other Works Consulted
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
Current as of: May 29, 2019
Author: Healthwise Staff
Sarah Marshall MD - Family Medicine
Brian D. O'Brien MD - Internal Medicine
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Kathleen Romito MD - Family Medicine
Kirtly Jones MD - Obstetrics and Gynecology
Current as of: May 29, 2019