Analytical sensitivity of four HIV combined antigen/antibody assays using the p24 WHO standard

Abstract

Background: The Common Technical Specifications for HIV-1 p24 assays published in 2009 fixed the lower limit of detection for obtaining C.E. approval at 2 IU/ml against the WHO standard (first international reference, code NIBSC 90/636); it was previously 50 pg/ml. Some recent fourth generation HIV assays that simultaneously detect antigen and antibody are equivalent to p24 assays, but they were mainly evaluated using p24 antigen standards in pg/ml and little is known of their performance with the IU/ml standard.

Objectives: To evaluate four of the combined serological assays most commonly used for HIV diagnosis in France against the WHO standard in IU/ml.

Study design: The analytical sensitivity of four combined p24 antigen and antibody assays (ARCHITECT HIV Ag/Ab Combo, AxSYM HIV Ag/Ab Combo, VIDAS HIV DUO Quick and VIDAS HIV DUO Ultra) and of one p24 assay (VIDAS HIV p24 II) were determined using dilutions of the WHO standard.

Results: Four of the five assays had a lower limit of detection below 2 IU/ml: 1.24 for ARCHITECT Combo, 0.66 for VIDAS DUO Ultra, 0.43 for VIDAS DUO Quick and 0.73 to 1.15 for VIDAS p24, while that of AxSYM was close to 2 (1.94-2.25).

Conclusions: We have provided the first data on the lower limit of detection of HIV combined assays using the IU/ml WHO standard and demonstrated the need for a single international standard for comparing assays. We recommend the use of this approach in medical laboratory to validate on site their methods.