Jun 3, 2001
Dear Dr.Cohen, You recently responded to a post where you suggested that a lipa assay(LiPa) might be indicated because of a low.<1,000 vl.,Could you explain if this is a geno or pheno? Is it avail at the regular labs?(I use Quest) And how new is this?Today is my last day of taking meds(SUSTIVA/EPIVIR/ABC) and I'd like to do a geno after 3 weeks.Should I do the LiPa instead or in addition to this? Thank you,Luke
Response from Dr. Cohen
A LiPa is a sensitive genotype. And for the kind of questions we often have, like do you have one of the more common mutations to commonly used meds - it may be enough as a first test. But it is not common nor standard to use it - and I do not know who commercially is offering it where you are. Or if Quest is. But it is not a new test - it was one of the earlier versions of genotyping. And has been replaced by more commonly done assays since it only looks at a limited number of sites to assess for resistance.
However, sounds you are doing stopping three potent meds - what is likely to be an effective triple. I'll guess you are stopping while it is doing well e.g. viral load <50 copies - as a treatment interruption to either just take a break from cumulative drug exposure, or even to try to stimulate some more immune response. Resistance testing off meds that were recently working is certainly of some theoretic interest to make sure that HIV didn't create resistance while regrowing. But the news from research that is doing just this so far suggests that if HIV was sensitive before the stop, it will remain sensitive after the interruption. There is some lingering anxiety about the Sustiva compared to other meds given its longer half life - but most studies report that resistance to this during an interruption is a rare event. And even if it does occur, a standard genotype should be able to detect the mutations from the nonnukes. Assuming your viral load goes over 1000 at some point off meds, these standard tests will see the mutations of concern. And at least one commercial lab, at Consolidated labs, claims a sensitivity even at lower viral loads...
But if your viral load is <1000 off meds, either you don't need meds due to an effective immune response, or you just checked early in the process after an interruption, and can recheck in another few weeks. At which point you can check for any mutations as well.
Hope that helps.
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