AskDocQ: What does HIV viral load mean?

HIV viral load u=u fiona bisshop
Illustration: Amsnel Gorgonio

You’ve been cruising along with an undetectable HIV viral load for years. Suddenly – the horror – you go to your routine appointment and your doctor tells you there’s an actual detectable number for your virus.

Maybe 30, 50 or 100, instead of the usual <20 result. It’s OK your doc says, it’s nothing to worry about, it’s just the new assay the lab is using.


Viral load refers to the number of copies of virus detectable in your bloodstream. It’s measured by a sophisticated lab machine and reported as how many millions of copies per ml they could measure.

As with all technology, it has improved over time, and the lab assays have become more sensitive.

Imagine counting sheep on a distant hillside through an ancient telescope. Then one day, someone gives you a fancy new set of binoculars.

Suddenly you see sheep you never saw before.

They’re not new sheep. They were always there, but out of sight of your old telescope.

The newer assays now used for detecting virus are a bit like a new set of binoculars.

What does your HIV viral load mean?

So, what does it actually mean to have a viral load of 30 or 50? Well here’s what it doesn’t mean? It doesn’t mean your meds are failing or your virus is resistant.

If you are good at remembering to take your meds, then resistance is extremely unlikely to develop.

If your viral levels are not going up, up, up at each follow-up test, then you do not have treatment failure.

But if the meds are working then why is there any virus detectable at all?

Remember that HIV infects immune system cells called CD4 T cells. While many cells die after they are infected, thus lowering your CD4 count, some of these cells live a very long time.

Eventually, they do die, and the virus contained within them is released, and may be detected. However, if you’re on effective meds then this newly released virus can’t actually infect any other cells. So, it can’t replicate.



Now your next question is going to be about U=U (undetectable equals untransmittable) and contagion risk, right?

The good news is that in the huge studies looking at this, the cut-off used for undetectable was 200, not 20 or 50 or even 100.

Your low-level viraemia is irrelevant and does not put your sexual partner at risk. Persistent viral loads above 200 are another story, however.

No doubt your doctor will do resistance tests in this situation and will advise condoms or PrEP for your partner.

The take home message is that sudden new low-level virus detection if you’re usually undetectable and take your meds is definitely not a disaster. You should not freak out!

Dr Fiona Bisshop specialises in LGBTIQ health. For more by Dr Bisshop visit, follow @DrFionaBisshop on Twitter, or send your health questions to

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