Rapid tests should be used in combination

An evaluation of eight rapid diagnostic tests widely used in a variety of African countries by Médecins Sans Frontières (MSF) shows that the tests vary in their performance, with false positive results being a concern.

Samples from some geographical locations were more likely to have false positive results than others, suggesting that tests need to be locally validated, and researchers report in the Journal of the International Aids Society.

False negative results were rare.

The findings confirm that the diagnosis of HIV should not be based on results from a single HIV rapid diagnostic test. A combination of HIV tests, and more specifically an algorithm (sequence) of two or three different HIV rapid tests, is required to make an HIV-positive diagnosis. This is already recommended by the World Health Organisation (WHO).

Misdiagnosing someone as having HIV can cause psychological trauma and profound social effects. Marriages may break down and people may take HIV treatment which they do not need.

Rapid diagnostic tests (RDTs) are the main diagnostic tool for HIV screening and diagnosis in resource-constrained settings. Despite their widespread use, there has been no systematic, head-to-head evaluation of their accuracy with specimens from diverse settings across sub-Saharan Africa. Experience from the field has suggested that, in some settings, some RDTs have sensitivities and specificities that are inferior to those recorded in WHO evaluations.

Venous blood samples were collected from 2 785 people attending six clinics in Guinea, Cameroon, Democratic Republic of Congo, Uganda (two clinics) and Kenya. These samples were frozen and sent to a laboratory in Belgium where they were tested with eight different RDTs. Because all tests were done in one location, it is unlikely that any differences in performance could be attributed to user variation, storage conditions or other methodological factors. Tests were performed and interpreted according to the manufacturer’s instructions, with each test being read by two laboratory technicians separately.

The other key measure of test accuracy is specificity, in other words, the percentage of results that will correctly provide a negative result when HIV is not present. Lower rates of specificity will produce more false positive results.

A separate analysis, in Clinical Infectious Diseases, highlights the dangers of HIV treatment programmes not routinely re-testing individuals before they begin treatment. Although re-testing is recommended by WHO, only 2 of 48 national testing policies that were surveyed recommended re-testing before initiating antiretroviral therapy.

It is important to ensure accurate testing to avoid ethical, personal, and social consequences of incorrect diagnosis and treatment for an HIV-negative person, the quality-of-life implications of unneeded regular treatment and potential associated toxicities, and the potential undermining effects of misdiagnosis for confidence in the health system more widely.

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