HIV serology signal-to-cutoff ratio as a rapid method to predict confirmation of HIV infection

Early and rapid detection of patients with HIV is a key to preventing further transmission. The purpose of this study was to assess the ability of signal-to-cutoff (S/CO) ratio from initial screening fourth-generation HIV serology to predict subsequent confirmation of HIV. Patients with a first-time positive HIV serology (S/CO ratio ≥ 1) from 2012 to 2016 were included. Ratios were compared to the results of confirmatory testing. Predictive probabilities (PPs) of a positive confirmatory result were calculated based on a logistic regression model. A total of 45,138 HIV serology tests were performed; 250 patients met inclusion criteria, comprising 84 (34%) HIV negative patients, 136 (54%) chronic infections, and 30 (12%) acute infections. The PP of a confirmed positive result increased with higher S/CO ratios, with a PP of 100% for a S/CO of 55 (95% CI 95–100). This study enables a more informed discussion of the probability of HIV infection, based on HIV serology S/CO thresholds, prior to a confirmatory result.