A toxoplasmosis test can determine whether or not a person is or has been infected with toxoplasmosis. During the test, blood or tissue samples are taken from a patient. By examining these samples, doctors can find evidence of Toxoplasma gondii, the parasite that causes the toxoplasmosis infection. If toxoplasmosis is found, a doctor can prescribe a treatment, though in an otherwise healthy patient, the disease will usually work itself out.
If a patient is currently infected with toxoplasmosis, the disease can be diagnosed by direct observation of the parasite. One way doctors search for living parasites is by collecting a tissue biopsy and staining the tissue sample. Observing this sample under a microscope will show the presence of the parasite. This toxoplasmosis test is rarely used because the disease is not often serious, and collecting tissue samples can be distressing to the patient. It also is possible to observe the parasites in a blood sample, though they are difficult to find.
Pregnant women who may be at risk for passing toxoplasmosis on to their unborn baby can also receive a molecular test of amniotic fluid. In this test, amniotic fluid is extracted from the uterus and tested for the presence of the parasite’s deoxyribonucleic acid (DNA). This is a more common toxoplasmosis test because the parasite can lead to serious complications in newborns.
Usually, a simple serologic toxoplasmosis test is used to diagnosis the disease. In this test, a blood sample is taken from a patient, and a test is done to measure the presence of the antibody immunoglobulin G. This will let the doctor know that the patient has at one point been infected with toxoplasmosis, though it will not indicate whether or not the parasite is still present; the presence of antibodies to toxoplasmosis means that a patient is either currently fighting off an infection or that they have fought it off in the past. An otherwise healthy adult can only become infected with toxoplasmosis once in their lifetime, so the presence of the antibody also indicates immunity.
If it is important to know when infection occurred, a toxoplasmosis test measuring immunoglobulin M and an avidity test may be used. This may be necessary for women who are pregnant or planning on becoming pregnant. An avidity test helps doctors know when an infection took place by observing the virulence of the antibody; antibodies that developed to fight off recent infections will behave more aggressively when confronted with a subsequent infection. These tests are also performed in a lab after obtaining a blood sample from the patient.