Health Encyclopedia

Toxoplasma test

Definition

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

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 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 to detect toxoplasmosis infection in a newborn baby. It may also be used to screen pregnant women for the antibodies to Toxoplasma. 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.

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.

What abnormal results mean

A titer of 1:16 - 1:256 indicates a probable previous infection. 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

Cohen J, Powderly WG. Infectious Diseases. 2nd ed. New York, NY: Elsevier; 2004.

Mandell GL, Bennett JE, Dolin R. Principles and Practice of Infectious Diseases. 6th ed. London: Churchill Livingstone; 2005.

Review Date:8/6/2007
Reviewed By:D. Scott Smith, MD., MSc., DTM., Prof. Medical Microbiology & Immunology, Dept. of Human Biology, Stanford Univ. School of Medicine, Stanford, CA. Review provided by VeriMed Healthcare Network.

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