What does WHO recommend to provide an accurate HIV diagnosis and prevent misdiagnosis?

What does WHO recommend to provide an accurate HIV diagnosis and prevent misdiagnosis?
A) Always use WHO HIV testing strategies.

A single HIV test result cannot provide a definitive HIV-positive diagnosis. Countries should follow WHO recommended testing strategies based on HIV prevalence of the population being tested—either high (≥5%) HIV prevalence or low (<5%) HIV prevalence—to help inform the validation of national HIV testing algorithms. These algorithms need to be validated at a national or regional level as test kit performance can vary across populations and settings. See explanation of testing strategies below.

Effective methods for validation have been presented at national and regional levels, including from Brazil, Senegal and the Pacific Island nations, among others. Guidance on how to validate national HIV testing algorithms can be provided by the WHO Prequalification of medicines and HIV Department.

See diagrams and link below on WHO-recommended testing strategies:

WHO recommendations to assure HIV testing quality
Policy brief - July 2015 - pdf, 117kB

Further guidance on the use of 4th generation tests or supplementary assays within a testing algorithm are available here:

Consolidated guidelines on HIV testing services
Chapter 7 - pdf, 4MB

And additional guidance is also available here:

Annex 7: Diagnostics for HIV diagnosis
Consolidated guidelines on HIV testing services - pdf, 483kB

High prevalence settings (≥5%) should use the following testing strategy:
High prevalence settings (≥5%) should use the following testing strategy.

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In a high (≥5%) HIV prevalence setting, two sequential positive (reactive) test results are needed to provide a person with an HIV-positive diagnosis.

In high prevalence settings (≥5%), HIV test results which are A1+, A2-, A3- are considered as HIV-negative. Report HIV-inconclusive, if A1 is 4th generation assay (retest in 14 days).

In high prevalence settings (≥5%), HIV test results which are A1+, A2-, A3+ are consider HIV-inconclusive and should be retested in 14 days to rule in or rule out seroconversion.
Low prevalence settings (<5%) should use the following testing strategy:
Low prevalence settings (<5%) should use this testing strategy

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In a low (<5%) HIV prevalence setting, three sequential positive (reactive) test results are needed to provide a person with an HIV-positive diagnosis.

In low prevalence settings (<5%) in the population being tested, HIV test results which are A1+, A2+, A3- are considered HIV-inconclusive and should be retested in 14 days to rule in or rule out seroconversion.

In low prevalence settings (<5%) in the population being tested, HIV test results which are A1+, A2-, consider patient HIV-negative, if A1 is 2nd or 3rd generation assay. Report HIV-inconclusive, if A1 is 4th generation assay (retest in 14 days).
B) WHO recommends that all people who have been diagnosed HIV-positive should be retested for HIV prior to antiretroviral therapy initiation.

WHO recommends that all people who have been diagnosed HIV-positive should be retested for HIV prior to antiretroviral therapy initiation. This is an effective and cost-effective way to reduce the risk of misdiagnosis and incorrect initiation of treatment for people who are truly HIV-negative.

The cost of not re-testing: HIV misdiagnosis in the art ‘test-and-offer’ era
pdf, 763kb
CROI 2017: Poster - pdf, 745kB

However, retesting should not be a barrier to immediately offering antiretroviral therapy (“Treat All”). Retesting can be performed the same day as the first HIV-positive diagnosis, using a separately collected second specimen, ideally with a second testing provider and if feasible, another facility or different site in the same facility.

Read information note on WHO's recommendation to re-test all newly dignosed people with HIV

C) WHO recommends that people who are taking antiretroviral therapy should not be re-tested for HIV.

This is because antiretroviral therapy works to supress the virus. So, when someone is responding well to treatment they will have undetectable levels of HIV in their blood, and may then also have low levels of HIV antibodies – the molecules which are detected by the commonly used HIV tests – and therefore have a “false” negative test result.