Test Overview
A
toxoplasmosis test is a blood test that checks for
antibodies to the Toxoplasma gondiiparasite. Your body's natural defense 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.
To see if your growing baby is
infected, the test can be done on a sample of the fluid that is around your
baby (amniotic fluid) taken during
amniocentesis.
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.
- Apply pressure to the site and then 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.
Risks
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.
Ongoing bleeding can be a problem for people with bleeding
disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can
make bleeding more likely. If you have bleeding or clotting problems, or if you
take blood-thinning medicine, tell the doctor before your blood is
drawn.
Results
A
toxoplasmosis test is a blood test that checks for
antibodies to the Toxoplasma gondiiparasite. The results of the test are usually given in
titers. A titer 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 titer 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 titer of 1 to 128 means there are
more toxoplasmosis antibodies in the blood than a titer 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.
Normal results1| Antibody | Titer |
|---|
IgM in babies: | Undetectable |
IgM in adults: | Less than 1:64 |
IgG: | Less than 1:1024 |
Toxoplasmosis antibodies usually form within 2 weeks after
being infected. The titer is the highest 1 to 2 months after infection.
- If high titers of the IgM type of antibody are
found, it means the infection is recent. If high titers 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 titers 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 Toxoplasmosis, Other, Rubella, Cytomegalovirus, and
Herpes. The TORCH test checks to see if your baby has
any of these infections.
- For more information on toxoplasmosis
infection in pregnancy, see the topic
Toxoplasmosis During Pregnancy.
- 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).
References
Citations
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Saunders.
Other Works Consulted
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Saunders.
- 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.
Credits
| By | Healthwise Staff |
|---|
| Primary Medical Reviewer | Sarah Marshall, MD - Family Medicine |
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| Specialist Medical Reviewer | Kirtly Jones, MD, MD - Obstetrics and Gynecology |
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| Last Revised | June 2, 2011 |
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