‘Viral load’ is the amount of HIV in your blood. You’ll have this tested regularly as part of your care to manage the virus. A viral load test on someone’s blood gives a good idea of how much HIV is in their semen or vaginal fluid too.
A person with HIV who is taking treatment and has an undetectable viral load cannot pass on HIV - although it can take up to six months on treatment to become undetectable.
Yes. If you’re taking HIV medication and have an undetectable viral load, you can’t pass on HIV.
A large study called PARTNER looked at 888 gay and straight couples (and 58,000 sex acts) where one partner was HIV positive and one was HIV negative. Results found that where the HIV positive partner was on treatment had an undetectable viral load, there were no cases of HIV transmission whether they had anal or vaginal sex without a condom.
The PARTNER study looked at couples where the HIV positive partner had a viral load below 200. An undetectable viral load is classed as being below 20 copies/ml.
The Partners PrEP study looked at the risk of transmission in the time it took for the HIV positive partner to achieve an undetectable viral load. In most cases (84.8%) this happened within six months and there were no infections once someone had been on treatment for six months or more.
The result is measured in copies (of the virus) per millilitre (ml) of blood and it can range from over 1,000,000/ml to fewer than 20/ml. Your doctor is likely to describe your viral load using just the number. For somebody not on HIV treatment, a viral load above 100,000 is considered high and one below 10,000 is considered low.
The aim of effective treatment is to reduce your viral load to undetectable levels (which can take up to six months), so that you can't pass on HIV.
An undetectable viral load doesn't mean there's no HIV present - HIV is still there but in levels too low for the laboratory test to pick up. Different laboratories may have different cut off points when classifying undetectable viral load, but most clinics in the UK classify undetectable as being below 20 copies/ml.
National guidelines recommend that everyone with HIV starts treatment right away.
This recommendation reflects the findings of the START study. It found that people who delayed treatment until their CD4 count dropped to 350 - which is when people were previously advised to start treatment - had a significantly higher chance of developing AIDS-related illnesses such as cancers.
Starting treatment will protect your health and reduce your viral load to undetectable levels. Early diagnosis and treatment means people living with HIV can expect to live as long as the general population.
For further information on CD4 count and viral load, see the Viral load and CD4 count page in our Simple Science section.
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by Anna Peters
Date due for the next review: 25/2/2020
Content Author: Richard Scholey
Current Owner: Health Promotion
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