Performance characteristics of the Cavidi ExaVir viral load assay and the ultra-sensitive P24 assay relative to the Roche Monitor HIV-1 RNA assay

Abstract

Background: The Cavidi viral load assay and the ultra-sensitive p24 antigen assay (Up24 Ag) have been suggested as more feasible alternatives to PCR-based HIV viral load assays for use in monitoring patients infected with HIV-1 in resource-limited settings.

Objectives: To describe the performance of the Cavidi ExaVir Load™ assay (version 2.0) and two versions of the Up24 antigen assay and to characterize their agreement with the Roche Monitor HIV-1 RNA assay (version 1.5).

Study design: Observational study using a convenience sample of 342 plasma specimens from 108 patients enrolled in two ACTG clinical trials to evaluate the performance characteristics of the Up24 Ag assay using two different lysis buffers and the Cavidi ExaVir Load™ assay.

Results: In analysis of agreement with the Roche assay, the Cavidi assay demonstrated superiority to the Up24 Ag assays in accuracy and precision, as well as sensitivity, specificity, and positive and negative predictive values for HIV-1 RNA ≥ 400, ≥ 1000 and ≥ 5000 copies/mL. Logistic performance curves indicated that the Cavidi assay was superior to the Up24 assays for viral loads greater than 650 copies/mL.

Conclusions: The results suggest that the Cavidi ExaVir Load assay could be used for monitoring HIV-1 viral load in resource-limited settings.