by Claire Taylor

Dr Sara Day, Sophie Jones. Chelsea & Westminster Hospitals NHS Foundation Trust.


Online postal testing services now represent the largest provider of HIV tests in London. Since SHL launched in
2018 >10,000 reactive HIV test results have been provided. We describe how using the cut-off index (COI) helps clinicians manage the expectations of service users receiving reactive HIV results.


SHL use the Roche Elecys HIV Duo test on self-sampled capillary blood (sensitivity 100%, specificity 99.87%). Due to a limited volume of capillary blood available service users with low reactive (COI <10) and reactive (COI ≥10) HIV results are all encouraged to have confirmatory testing performed, preferably at a sexual health clinic (SHC).

Since the pandemic, recipients of low reactive results that do not report significant HIV risk are given the option to repeat the SHL HIV test kit instead of attending SHC for confirmatory testing. Those with a reactive HIV screening result are still encouraged to attend SHC.

The confirmatory outcomes of reactive results received 01/05/2019–01/09/2022 and low reactive results received 01/01/2021–01/01/2022, were identified from an e-note review.


Of 534 reactive screening results the confirmatory tests comprised 297 (56%) positive, 169 (31%) negative,
68 (13%) not known. 466/534 (87%) received confirmatory testing.Where confirmation outcomes are
known 64% confirmed positive.

Of 1314 low reactive screening results the confirmatory tests comprised 23 positive (1%), 1107 (84%) negative and 184 (14%) not known. 1130/ 1314 (86%) received confirmatory testing. Where confirmation outcomes are known 2% confirmed.

All service users confirmed with previously undiagnosed HIV infection were linked to HIV outpatient care.


With low and decreasing national positivity rates of undiagnosed HIV and increasing numbers of individuals testing using online services, more false reactive HIV results may be generated which can be distressing to service users and challenging for clinic staff to manage. Using COI can be used by SHL staff and clinic staff to anticipate the confirmatory outcome of reactive HIV results. Offering repeat SHL test kits to low-risk individuals with low reactive HIV results, as a means of confirmatory testing, helps minimise unnecessary clinic visits and appears to be a preferred choice for many service users.

About the author:

Claire is the Senior Digital Marketing Executive at Preventx.