O24 Quantitative reactive values to support HIV result notifications on small blood volumes from self-sampling test kits

Abstract

Introduction

HIV tests on small blood samples complete the first stage only of the usual 3 stage HIV testing confirmatory algorithm. For this reason, false positive rates are high. Quantitative reactive values could support counselling when giving these results. We looked at reactive values for confirmed/unconfirmed positives to guide use of reactivity rates in results notification.

Methods

We analysed routinely collected data from all HIV self-sampling tests completed within SH:24 during 2022 including reactivity value and the outcome of confirmatory testing. Standard practice for notifying users is 6 contact attempts using 3 different means of communication. The results of confirmatory testing are obtained from the user or the service attended.

Results

257,143 HIV tests were done in 2022 of which 966 (0.4%) were reactive. The results of confirmatory testing were available in 818 (84.68%) and 141 reactives were confirmed positive of which 85 were new diagnoses. Reactivity values ranged from 1.0 - 2713. The positive predictive value (PPV) for all reactives 0.17 and the PPV for reactives over 30 was 0.9.

Discussion

Self-testing is an important source of new HIV diagnoses. While some confirmed positives had reactivity value less than 30, a reactive value over 30 is an important factor in counselling those with self-sampling test results.