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→Laboratory Tests
acute Atypical lymphocytosis, mild anemia, leukopenia, and slightly elevated liver enzymes are common. The syndrome may persist for weeks but is almost always self-limited.
acute Atypical lymphocytosis, mild anemia, leukopenia, and slightly elevated liver enzymes are common. The syndrome may persist for weeks but is almost always self-limited.
The diagnosis is usually made serologically using an indirect fluorescent antibody (IFA) test or enzyme immunoassay (EIA) for IgG and IgM antibodies. Specific IgM antibodies appear during the first 2 wk of acute illness, peak within 4 to 8 wk, and eventually become undetectable, but they may be present for as long as 18 mo after acute infection. IgG antibodies arise more slowly, peak in 1 to 2 mo, and may remain high and stable for months to years. Specific IgM antibodies with low IgG are consistent with recent infection in immunocompetent patients. Acute infection should also be suspected if the IgG is positive in an immunocompromised host with encephalitis. Toxoplasma-specific IgG antibody levels in AIDS patients with Toxoplasma encephalitis are usually low to moderate but may be absent; IgM antibodies are not present. Past infection in a healthy person typically produces a negative IgM test, and a positive IgG test. In patients with retinochoroiditis, low titers of IgG antibodies are usually present, but IgM antibodies are not detected.
The diagnosis of acute toxoplasmosis during pregnancy and in the fetus or neonate can be difficult, and consultation with an expert is recommended. If the patient is pregnant and IgG and IgM are positive, an IgG avidity test should be done. High avidity antibodies in the first 12 to 16 wk of pregnancy essentially rules out an infection acquired during gestation. But a low IgG avidity result cannot be interpreted as indicating recent infection because some patients have persistent low IgG avidity for many months after infection. Suspected recent infection in a pregnant woman should be confirmed before intervention by having samples tested at a toxoplasmosis reference laboratory. If the patient has clinical illness compatible with toxoplasmosis but the IgG titer is low, a follow-up titer 2 to 3 wk later should show an increase in antibody titer if the illness is due to acute toxoplasmosis, unless the host is severely immunocompromised.
===Diagnostic Imaging===
===Diagnostic Imaging===