Toxoplasma antibodies - serum

Last updated: Sunday, 28, May, 2006

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Item Process
Specimen

5-10 mL blood in plain tube.

Method

EIA, IFA.

Reference Interval

IFA IgG titre <16.

Application

Diagnosis of suspected toxoplasmosis, eg:
glandular fever-like syndromes;
hepatitis;
fever in immunosuppressed patients (including HIV infection);
retinitis;and
TORCH syndrome in neonates.

The test is appropriate in the initial assessment of patients with newly diagnosed HIV infection.

Interpretation

A four fold rise in IgG titre between acute and convalescent samples (taken at least 2 weeks apart) is diagnostic for toxoplasmosis. The response may take up to 8 weeks to peak.

Titres of 16 to 64 may persist for life. IgM antibody at a titre of >16 indicates infection probably within the past year.

If determination of the time of infection is critical eg, in pregnancy, IgG avidity studies may be indicated.

The diagnosis of congenital toxoplasmosis in the neonate is supported by the presence of IgM antibodies.

Serological testing is not useful for determination of active central nervous system toxoplasmosis in immunocompromised patients.

PCR testing of body fluids (CSF, amniotic fluid) or tissues may provide evidence of active disease.

Reference

Montoya JG. J Infect Dis 2002; 185: 73-82.

Montoya JG. J Clin Microbiol 2002; 2504-2508.