Use of the p24 Antigen to Evaluate Virological Failure among HIV-1-Infected Patients Receiving Antiretroviral Treatment in Tanzania

Background: In many resource-limited settings, virological monitoring of HIV-infected patients receiving combination antiretroviral therapy (cART) is not routinely available due to the high cost of HIV-RNA measurements. We aimed to examine whether a p24 antigen-based assay can be used as an alternative and cheaper method to monitor HIV treatment. Methods: Samples collected in conjunction with a study at Muheza Designated District Hospital, Tanzania, investigating possible interactions between HIV drugs and antimalarials, were retrospectively analysed for HIV load (HIV-RNA and p24 antigen). HIV-infected patients, who had received cART>180 days were included in this cross sectional study. Plasma p24 antigen levels were measured by PerkinElmer p24 ultrasensitive assay and HIV-RNA by COBAS® AmpliPrep/COBAS® TaqMan® HIV-1 test. We analysed the use of p24 antigen results as a predictor of cART response, where cART treatment failure was defined as HIV-RNA ≥ 1,000 copies/mL. Results: Two-hundred-and-sixty-six patients, who had been on cART for a median of 2.7 years (IQR: 1.7-3.8), were included. Eighty-eight percent had HIV-RNA<1,000 copies/mL and 40% had undetectable p24 antigen. There was only a weak correlation between HIV-RNA and p24 antigen (R2 =0.35), but undetectable p24 antigen had a high negative predictive value for treatment failure (99%). If only positive p24 antigen tests were re-analysed by PCR technique, costs for treatment monitoring could be substantially reduced. Conclusion: The p24 antigen assay might be useful to improve access to virological monitoring of HIV-infected patients in resource-limited countries.