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Development of novel cytomegalovirus and toxoplasma IgG avidity assays using an antigen competitive format "AVIcomp" on the Abbott ARCHITECT Instrument

Abstract number: p879

Maine  G.T., Hsu  S., Smith  D., Curdt  I., Herzogenrath  J.

Objectives: 

Development of novel Cytomegalovirus (CMV) and Toxoplasma (Toxo) IgG avidity assays using an antigen competitive "AVIcomp" format on the automated ARCHITECT instrument.

Methods: 

Conventional IgG avidity assays for a variety of infectious diseases employ chaotropic reagents, for example, urea or diethylamine, to distinguish between antibodies of low and high avidity. The AVIcomp competitive assay format does not use chaotropic reagents but relies on mass action using aqueous antigen to discriminate between low and high avidity antibodies. Two IgG assays were performed in the AVIcomp format to determine the Avidity Index (AI) on the ARCHITECT instrument as follows. In Assay No. 1, the patient sample was pretreated with buffer and in Assay No. 2 the patient sample was pretreated with aqueous CMV (viral lysate) or Toxo (purified MBP-P30 (SAG1)) antigen. Pretreatment of the patient sample with aqueous antigen blocks binding of high avidity IgG antibodies to the solid phase in the subsequent assay step. Microparticles coated with CMV or Toxo antigens were then added to each assay, washed, and anti-human IgG conjugate was then added and signal generated. The ratio of the signal in Assay No. 2 over the signal in assay No. 1 was proportional to the amount of low avidity anti-CMV or anti-Toxo IgG present in the patient sample. Since the Avidity Index for an avidity assay is defined as the proportion of high avidity antibodies present in the patient sample, the results of the AVIcomp assay were transformed mathematically as follows: AI(%) = [1-(Signal Assay No. 2/Signal Assay No. 1)] × 100.

Results: 

The preliminary results of the ARCHITECT CMV IgG avidity assay and the ARCHITECT Toxo IgG avidity assay were compared to the Radim CMV IgG and Vidas Toxo IgG avidity assays, respectively, by testing seroconversion panels, pregnant women and random blood donor patient populations. The relative agreement between the ARCHITECT and Radim CMV IgG assays was 98.7% with a correlation coefficient r = 0.88. The relative agreement between the ARCHITECT and Vidas Toxo IgG assays was 100% with a correlation coefficient r = 0.97.

Conclusion: 

These preliminary results suggest that the performance of the novel CMV and Toxo IgG avidity assays employing AVIcomp technology was equivalent to conventional avidity assays using chaotropic reagents.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Subject:
Location: Oxford, UK
Presentation type:
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