Neutralization assay to resolve discrepancies between positive results in new highly sensitive anti-Toxoplasma gondii IgG assays and negative results in reference tests

• Published in: European journal of clinical microbiology & infectious diseases 2010-03, Vol.29 (3), p.359-363
• Main Authors: Köhler, S., Rößler, D., Hornauer, S., Upmeier, B., Franck, J., Liesenfeld, O.
• Format: Article
• Language: English
• Subjects: Antibodies, Protozoan - blood; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Brief Report; Diagnostic Errors; Enzyme-Linked Immunosorbent Assay; Female; Human protozoal diseases; Humans; Immunocompromised Host; Immunoglobulin G - blood; Infectious diseases; Internal Medicine; Medical Microbiology; Medical sciences; Neutralization; Neutralization Tests - methods; Parasitic diseases; Pregnancy; Protozoal diseases; Sensitivity and Specificity; Toxoplasma; Toxoplasma - isolation & purification; Toxoplasmosis; Toxoplasmosis - diagnosis; Toxoplasmosis - immunology
• ISSN: 0934-9723; 1435-4373
• DOI: 10.1007/s10096-009-0864-8

High sensitivity of IgG assays is required in order to diagnose Toxoplasma infection in immunocompromised patients and women before and during early pregnancy. Positive results obtained in new highly sensitive Toxoplasma IgG assays have been observed in sera that gave negative results in reference assays. To allow the resolution of these discrepancies, we developed a neutralization assay using 80 µg/ml of a soluble membrane fraction of Toxoplasma in the automated Elecsys IgG assay. We were able to block the detection of Toxoplasma IgG antibodies in 283 sera with IgG titers ranging from below the limit of detection to >2,300 IU/ml. The mean percentage of neutralization was 88%, with a minimum neutralization of 77%. In summary, the neutralization assay represents a valuable tool to confirm the specificity of Toxoplasma IgG antibodies in the sera of immunocompromised patients and women before and during early pregnancy. Discrepancies between positive results in highly sensitive Toxoplasma IgG assays and negative results in reference assays can, thereby, be resolved and may allow a decision to be made on the management of patients.