A blood test (taken regularly by your HIV doctor) that measures the number (amount) of HIV virus particles (copies) circulating in the blood. The viral load test is also known as an HIV RNA test – which uses Polymerase Chain Reaction (PCR) laboratory test technology. Viral load tests are used to monitor the rate of HIV replication over time. This can help make decisions on when to start HIV antiretroviral therapy, or can indicate treatment failure if a sustained increase in viral load occurs (over at least 2 tests). Small rises in viral load (in the 100’s) are known as ‘blips’, and are not clinically concerning. Larger elevations in viral load (in the thousands) are more concerning, as it might indicate that your treatments aren’t working as well as they should – your doctor will assess this. Undetectable viral load is achieved when HIV antiretroviral therapy reduces the amount of HIV RNA virus copies in the blood to less than 40 copies (per ml of blood); although new ultrasensitive tests can now measure to below 20 copies (but the basic principle is the same – i.e. there is substantially less virus circulating in blood). The goal of HIV ARV treatment is to durably keep the viral load to undetectable levels (supressed to below 40 copies), to minimise damage to the body and immune system. Taking HIV ARV therapy every day commonly results in obtaining an undetectable viral load. because HIV antiretroviral treatments are highly effective in supressing the HIV virus. Having an undetectable viral load also substantially reduces the risk of transmission of (passing on) HIV.