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Tests and diagnosis
By Mayo Clinic staffMost pregnant women in the United States aren't routinely screened for toxoplasmosis, and most states don't screen infants for the infection. Without specific screening, toxoplasmosis is often difficult to diagnose because signs and symptoms, when they occur, are similar to those of more common illnesses such as the flu and mononucleosis.
Testing in pregnancy
If your doctor suspects you have the infection, you may have several blood tests that check for antibodies to the parasite. Antibodies are proteins produced by your immune system in response to the presence of foreign substances, including viruses, bacteria, parasites, drugs and toxins. Because these antibody tests can be difficult to interpret, the Centers for Disease Control and Prevention (CDC) recommends that all positive results be confirmed by a laboratory that specializes in diagnosing toxoplasmosis.
What test results mean
Sometimes you may be tested early in the course of the disease before your body has a chance to produce antibodies. In that case, you may have a negative result, even though you're infected. If your doctor is still suspicious, you'll need to be retested in several weeks. In most cases, though, a negative toxoplasmosis test result means you've never been infected and therefore aren't immune to the disease. If you're at high risk, you can take certain precautions so that you don't become infected in the future.
A positive result, on the other hand, doesn't necessarily mean you're actively infected. In many cases, it's a sign that you were infected at some time in your life and are now immune to the disease. Further tests can help determine when the infection occurred, based on the types of antibodies in your blood, and whether the levels of these antibodies are rising or falling. This is especially important if you're pregnant or living with HIV/AIDS.
Testing your baby
If you're pregnant and have a current toxoplasmosis infection, the next step is to determine whether your baby also is infected. Tests your doctor may recommend include:
- Amniocentesis. In this procedure, which can be done safely after 15 weeks of pregnancy, your doctor uses a fine needle to remove a small amount of fluid from the fluid-filled sac that surrounds the fetus (amniotic sac). Tests are then performed on the fluid to check for evidence of toxoplasmosis. The test carries a slight risk of miscarriage. You may also experience minor complications, such as cramping, leaking fluid or irritation where the needle was inserted.
- Ultrasound scan. This test uses sound waves to produce images of your baby in the womb. A detailed ultrasound can't diagnose toxoplasmosis, although it can show whether your baby has certain signs, such as hydrocephalus. But because most infants don't show signs of toxoplasmosis at birth, a negative ultrasound doesn't rule out the possibility of infection. For that reason, your newborn will need a thorough examination after birth and follow-up blood tests during the first year of life.
Testing in severe cases
If you've developed a life-threatening illness such as toxoplasmic encephalitis, you may need one or more imaging tests to check for lesions or cysts in your brain. These include:
- Magnetic resonance imaging (MRI). This test uses a magnetic field and radio waves to create cross-sectional images of your head and brain. During the procedure, you lie inside a large, doughnut-shaped machine that contains a magnet surrounded by coils that send and receive radio waves. In response to these radio waves, your body produces faint signals that are picked up by the coils and processed into images by a computer. MRI is noninvasive and poses no risks to your health.
- Brain biopsy. In rare cases, especially if you don't respond to treatment, a neurosurgeon may take a small sample of tissue from your brain. The sample is then analyzed in a laboratory to check for the presence of toxoplasmic cysts.
- Toxoplasmosis fact sheet. Centers for Disease Control and Prevention. http://www.cdc.gov/toxoplasmosis/factsheet.html. Accessed May 5, 2009.
- Martin-Rabada P, et al. Blood and tissue protozoa. In: Cohen J, et al. Infectious Diseases. 2nd ed. New York, N.Y.: Mosby; 2004. http://www.mdconsult.com/das/book/body/135708454-2/0/1209/737.html?tocnode=49359306&fromURL=737.html#4-u1.0-B0-323-02407-6..50247-6--cesec17_8111. Accessed May 4, 2009.
- Kasper LH. Toxoplasma infections. In: Fauci AS, et al. Harrison's Principles of Internal Medicine. 17th ed. New York, N.Y.: McGraw-Hill Medical; 2008. http://www.accessmedicine.com/content.aspx?aid=2896423. Accessed May 4, 2009.
- McLeod R, et al. Toxoplasmosis (toxoplasma gondii). In: Kleigman RM, et al. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa.: Saunders Elsevier; 2008. http://www.mdconsult.com/das/book/body/135783748-2/0/1608/732.html?tocnode=54480801&fromURL=732.html#4-u1.0-B978-1-4160-2450-7..50289-9_6064. Accessed May 4, 2009.
- Toxoplasmosis. March of Dimes. http://www.marchofdimes.com/professionals/14332_1228.asp. Accessed May 6, 2009.
- Centers for Disease Control and Prevention, et al. Preventing congenital toxoplasmosis. MMWR Recommendations and Reports. 2000;49:57. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr4902a5.htm. Accessed May 8, 2009.
- You can prevent toxo. Centers for Disease Control and Prevention. http://www.cdc.gov/hiv/resources/brochures/toxo.htm. Accessed May 5, 2009.
- Montoya JG, et al. Diagnosis and management of toxoplasmosis. Clinics in Perinatology. 2005;32:705.
