Toxoplasma test

Definition

The toxoplasma test looks for antibodies in the blood to a parasite called Toxoplasma gondii. The parasite causes an infection called toxoplasmosis, which can be dangerous to a developing fetus and persons with AIDs.

Alternative Names

Toxoplasma serology; Toxoplasma antibody titer

How the test is performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

The sample is sent to a lab, where antibodies to Toxoplasma gondii are detected using several tests, including an indirect fluorescent antibody test, ELISA, and the Sabin-Feldman dye test.

How to prepare for the test

There is no special preparation for the test.

How the test will feel

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

The test is done soon after pregnancy to detect toxoplasmosis infection in a newborn baby. It may also be used to screen pregnant women for the antibodies to the parasite.

The presence of antibodies before pregnancy probably protects a fetus against toxoplasmosis at birth. However, antibodies that develop during pregnancy may mean possible infection of the baby, with an increased risk of miscarriage or birth defects.

This test may also be done to evaluate patients who have:

• Prolonged sore throat and swollen lymph nodes in the neck
• Unexplained lymph node swelling
• An unexplained rise in the blood white cell (lymphocyte) count
• HIV and have symptoms of a brain infection (including headache, seizures, weakness, and speech or vision problems)
• Unexplained inflammation of the back part of the eye (chorioretinitis)

Normal Values

A titer (measurement of the concentration in a sample) of less than 1:16 indicates that there has likely never been an infection with toxoplasma gondii.

What abnormal results mean

A titer of 1:16 - 1:256 is a sign that you have probably been infected with the parasite sometime in the past.

A titer of greater than 1:1,024 may indicate an active toxoplasmosis infection.

What the risks are

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

References

Liesenfeld O. Toxoplasmosis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 370.