• Serologic examination is used initially to indicate the presence of the infection by detecting Toxoplasma-specific antibodies.
• Serum, plasma, cerebrospinal fluid (CSF), and eye fluid specimens may all be tested for antibodies. If determination of immune status is the reason for testing, a single specimen is satisfactory.
• If determining the time of infection is important, two specimens drawn at least 3 weeks apart may or may not be useful.
• In most cases, detection of a rising IgG or IgM titer is not possible because the titers have already reached a plateau by the time the initial sample is drawn.
• The above algorithm may be used to determine the appropriate sequence of serological testing."

-CDC (used with permission, public domain)