AIDS Treatment Update, Issue 61-62, January-February 1998
Edward King

Dr Moyle notes that "We know that with the standard viral load tests, most people who are going to go below 400 copies/ml will have done so by the time they've received 16 to 24 weeks of triple therapy. That makes it easy to say that if your viral load remains above 400 after 16 to 24 weeks, you should consider changing therapy. But we don't know how long it's likely to take to go below detection using the ultra-sensitive test. That means there's a real risk of leaping to the wrong conclusions."

Throughout the first year of triple therapy with AZT/3TC/indinavir in the Merck 035 trial, participants' viral load fluctuated around the limit of detection of the ultra-sensitive test; for instance, an individual would have below 50 copies/ml one month, but the next month it would be detectable at, say, 60 to 70 copies/ml, before dropping back below the limit of detection after another month.

But after about a year of treatment, most people whose viral load remains undetectable using standard assays (i.e. it is somewhere below zero and 400 copies/ml) do turn out to have below 50 copies/ml when tested with the ultra-sensitive test. Only a very small proportion fall into the 50 to 400 copies/ml zone.

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