Analytical performance of the VITA™ point-of-care CD4 enumeration assay

Highlights
• Rapid point-of-care CD4 cell enumeration is critical for clinical management of HIV.
• The novel VITA ™ CD4 test provides a numeric CD4 count in 35 min.
• VITA™ CD4 results were strongly correlated with the gold standard, flow cytometry.
• The precision of VITA™ CD4 and its accuracy to identify advanced HIV were optimal.
• VITA™ CD4 is a promising tool for CD4 enumeration when infrastructure is limited.

Abstract
CD4+ T-cell enumeration remains critical for management of people with HIV (PWH). In resource-limited settings, point-of-care CD4 testing can increase accessibility and decrease turnaround time compared to flow cytometry. This study evaluated the performance of VITA™ point-of-care CD4 (Accesso Biotech; VITA™ CD4) compared to AQUIOS™ (Beckman Coulter; AQUIOS™) flow cytometry.

Remnant venous blood samples from PWH with known CD4 counts on FDA-cleared AQUIOS™ flow cytometry were tested twice with VITA™ CD4. Statistical analyses included descriptive statistics, correlation analysis, Bland-Altman agreement analysis, and Passing-Bablok regression. The coefficient of variation was calculated on duplicate measurements. The University of San Francisco Institutional Review Board approved the study.

VITA™ CD4 results showed strong correlation with AQUIOS flow cytometry (r = 0.973, p < 0.001). Bland-Altman analysis revealed a mean bias of −48.9 cells/μl (95% CI: −61.8 to −36.0), with limits of agreement from −231.1 to 133.3 cells/μl. For samples <500 CD4 cells/μL (n = 137), the mean bias was reduced to −8.6 cells/μl (95% CI: −17.8 to 0.6). Passing-Bablok regression suggested a small constant positive bias and proportional bias at counts above 500 cells/μl [y = 30.2 (95% CI: 19.3 to 44.2) + 0.83× (95% CI: 0.80–0.86)]. The coefficient of variation for duplicate VITA CD4 measurements was 11.86%.

VITA™ CD4 results correlated strongly with flow cytometry at clinically relevant CD4 values. Its diagnostic performance and applicability at point-of-care make it a promising CD4 tool, also in settings with limited laboratory infrastructure. Further clinical validation and assessment of user acceptability is recommended.