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HIV point-of-care tests (POCTs) are increasingly popular and overcome many barriers to testing. Yet POCTs have false reactive results requiring confirmation.
Teague et al, looked at using a second POCT as confirmation. The first line POCT was the INSTI HIV-1/HIV-2 rapid antibody test; the confirmatory test the Alere Determine. The serum of 91 individuals with a positive INSTI was retrospectively tested; Determine successfully identified all false reactive INSTIs.1
These data led us to introduce a testing algorithm using Determine (fourth generation) as rapid confirmation for all reactive INSTIs alongside the standard laboratory test. This letter presents a review of its use from January to December 2010.
In this period, 220 INSTI reactive patients received both confirmatory tests: 213 of these were reactive on Determine and laboratory tests confirmed HIV infection.
Seven had a negative Determine, with five proven to be false reactive by laboratory testing. However, two were found to be laboratory positive and were experiencing HIV seroconversion.
The results suggest reactive samples on both POCTs are extremely unlikely to be falsely positive.
Although all false-reactive INSTIs were identified by Determine, Determine missed two patients with HIV seroconversion. Determine now includes a p24antigen component. However, laboratory tests have a greater sensitivity so it is expected that Determine will miss some seroconverters; Rosenberg et al2 and Fox et al3 report the sensitivity of Determine in detecting acute HIV infection at 25% and 50%, respectively. Our data goes further; indicating that while Determine is currently the only fourth-generation POCT, there are instances where third-generation POCTs may detect infection earlier.
However, our data cannot say whether Determine could detect some acute infections that INSTI may miss.
Significantly, these data highlight the importance of running laboratory fourth-generation tests in parallel with POCTs when clinical history suggests acute HIV infection, and when there has been significant risk of HIV acquisition within the window period.
Contributors AM introduced the testing algorithm to the clinical service. AM and RS collected the data and analysed it. They wrote and submitted a poster to BASHH 2011. RS wrote this as the submitted report. AM is the main editor and is also involved with feedback. SM provided input on the format for our statistics.
Competing interests None.
Provenance and peer review Not commissioned; internally peer reviewed.