Newest Combination HIV Antigen-Antibody Assay Evaluated

A fourth-generation antigen-antibody combination assay has been developed to allow earlier detection of seroconversion, and has increased sensitivity and improved specificity.

Scientists at the Innsbruck University Hospital (Austria) determined how early the assay could detect infection compared with existing assays; whether all HIV variants could be detected; and the assay's specificity using samples from blood donors, routine specimens, and patients with potential cross-reacting factors.

The study was carried out at 12 centers in Europe, Thailand, and Australia. The Elecsys HIV combi PT assay (Roche Diagnostics; Penzberg, Germany) is performed according to the sandwich principle. The results are automatically determined by the Elecsys software that compares the signal produced from the sample with the cutoff value obtained during system calibration. The total assay time is 27 minutes.

A total of 14 seroconversion panels, comprising 135 samples were analyzed to determine how soon after a positive polymerase chain reaction (PCR) result the immunoassays could detect HIV infection. Samples were identified as positive by the Elecsys assay 4.9 days after a positive PCR result that had been predetermined, which was earlier than the 5.3 to 7.1days observed with other comparable assays. The analytical sensitivity of the Elecsys HIV combi PT assay for the HIV-1 p24 antigen was 1.05 IU/mL, which compares favorably with the other assays.

In addition, the assay identified all screened HIV subtypes and displayed greater sensitivity to HIV-2 homologous antigen and antibodies to HIV-1 E and O and HIV-2 than the other assays. The assay demonstrated 100% specificity in patients with infections other than HIV, such as Cytomegalovirus or herpes simplex virus. Overall, the specificity of the Elecsys assay was 99.88% using samples from blood donors and 99.81% when analyzing unselected samples. Potential cross-reacting factors did not interfere with assay performance. The Elecsys HIV combi PT assay has been granted the European Conformity (CE) marking and is now available for use in laboratory-based testing. The study was published in the February 2013 issue of the journal Medical Microbiology and Immunology.

Related Links:
Innsbruck University Hospital
Roche Diagnostics