Performance evaluation and optimized reporting workflow for HIV diagnostic screening and confirmatory tests in a low prevalence setting.

Background: Our institution utilizes an antigen/antibody screening test followed by a confirmatory antibody assay for preliminary positive results. Given the low prevalence for HIV infections in our institution's county, we suspect that a substantial portion of the reactive screens are false positives.

Objectives: We aimed to characterize the false positivity rate of the HIV screening test performed at Stanford Health Care. In parallel, we modified our reporting workflow to release both the screening and confirmatory results simultaneously to mitigate the stress of a presumptive positive test.

Study Design: We reviewed 45,296 eligible HIV screen specimens that underwent the Abbott ARCHITECT™ 4th generation HIV antigen/antibody combination assay between August 5, 2016 and March 16, 2021. Final sample signal/cutoff (S/CO) ratios ≥ 1 were deemed positive, which triggers a reflex order for the confirmatory Bio-Rad Geenius™ HIV 1/2 Supplemental Assay. Additional chart review was performed for positive screen cases with negative or indeterminate confirmatory results.

Results: Our institution demonstrated a 0.28% (128/45,296) positive screen rate, with 12.5% (16/128) of these samples confirmed as false positives based on a negative HIV-1 RNA test. Median S/CO ratios of true positive screens were significantly higher than those with negative or indeterminate confirmatory tests (602.27vs 2.98; p = 0.0000323). We implemented a new synchronized reporting system for positive screens, which co-releases screen and confirmatory reports without compromise in the overall turnaround time.

Conclusions: Our study demonstrates a relatively high percentage of false positive screens. Subsequently, by providing a more complete picture up front, our new reporting pipeline may reduce anxiety of a stand-alone positive screen and optimize downstream clinical decision-making.