Validation and performance of a rapid HIV-1 viral load assay

Current diagnostic algorithms for HIV-1 primarily depend on antigen-antibody tests, with nucleic acid tests reserved for confirmation and monitoring of antiretroviral therapy. Incorporating a quantitative nucleic acid test at the point of care could provide faster diagnosis and viral load measurement in a single clinical encounter, expediting linkage to care. This study evaluates the Xpert HIV-1 Viral Load XC (Xpert VL XC) assay as a candidate for primary nucleic acid testing use within HIV-1 diagnostic workflows, compared to standard-of-care approaches. The Xpert VL XC demonstrated a measurable analytical range of 60-1 × 10⁶ copies/mL (R² = 0.99) with 100% detection across tested concentrations. Precision analyses showed greatest variability at the lowest concentration, with acceptable assay reproducibility. Agreement analyses using 20 HIV-1 positive and 10 HIV-1 negative plasma samples showed 100% agreement compared to the Roche cobas HIV-1 (quantitative) assay. The Xpert VL XC was compared to four other HIV assays, including the Xpert HIV-1 Qual XC. The Xpert VL XC produced 3.2% invalid results and achieved negative agreement of ≥96.8%. Positive agreement ranged from 80.8% to 90.0%, with most discrepancies occurring below the 40 copies/mL lower limit of quantification threshold. The Xpert HIV-1 Qual XC was the only assay that detected all 26 samples that were positive using the standard immunoassay diagnostic algorithm. Average turnaround time was 3 h, faster than the 21 h average for conventional batch testing. These findings highlight the limitations of implementing rapid molecular HIV-1 diagnostics and the need for both sensitive and rapid approaches.IMPORTANCECurrent testing algorithms for the diagnosis of HIV-1 initially test samples with an antigen/antibody test followed by an antibody differentiation test if the screening test is positive. Nucleic acid tests are used to aid in the diagnosis (qualitative and quantitative assays) or monitoring a patient's response to antiretroviral therapy (quantitative). However, a quantitative diagnostic nucleic acid test may have additional utility, particularly in point-of-care settings, or near the patient care site. This would allow both diagnosis and initial viral load measurement to occur during a single visit, permitting rapid linkage to care. We evaluated the Xpert HIV-1 Viral Load XC test as a potential tool for primary nucleic acid testing within the HIV-1 diagnostic algorithm and assessed its suitability for use under the unique constraints of point-of-care environments.