HIV can become resistant to antiretroviral drugs. Drug resistance can develop if you are taking HIV treatment that does not fully suppress the virus, and it can cause your current HIV treatment to stop working effectively. Viral load, which should drop when you start a new drug combination, will increase again if drug-resistant HIV develops. This is one of the reasons why taking your treatment as prescribed (adherence) is so important.

Blood tests can tell whether strains of HIV are resistant to any anti-HIV drugs. In the UK, it is recommended that people have a resistance test before they first start HIV treatment. As a drug-resistant strain of HIV could be passed on, it is important to have this test to make sure that your treatment combination includes drugs that are effective against the strain of HIV you have. You should also have a resistance test if your viral load becomes detectable again, before you change your HIV treatment.

Resistance tests can only be done if your viral load is detectable. The tests most commonly used are thought to work best if your viral load is above 1000 copies/ml. Now researchers  have each done studies into how reliable resistance tests are for people with detectable, but low, viral loads. they found that resistance tests can give reliable results in this situation, even – in some cases – when someone’s viral load was below 200 copies/ml. In addition, doctors could use the test results to predict accurately whether someone’s viral load would continue to increase, suggesting treatment was not working.

The most important thing you can do to reduce your risk of developing drug resistance is to take your HIV treatment as prescribed (called adherence), to give it the best chance of working.

details of the study can be found here.