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how long is a resistance test good for??
Jul 1, 2003

I am treatment naive. I was diagnosed March 2003--last neg test March 2002. When I went for labs last week, I asked for pheno or geno test. While my doctor agreed, he was reluctant--stating that it may not be accurate at this point. Do those pheno and geno resistance tests become unreliable after some time? If so, how long are they effective for? Please respond--I wrote last week and have not heard back so I am directing this time to you Dr Young.

Response from Dr. Young

There isn't good information the accuracy of resistance tests in treatment naive persons, only that they are the most accurate early in infection.

Previously, the opinion was that there was little utility of testing in treatment-naive persons with chronic infection, based on the idea that the virus, even if resistant in the beginning, would revert back to wild type (drug sensitive) after some time.

There is a recent and growing appreciation that at least some mutant viruses can persist for quite a while, even in the absence of drug selection-- this is particulary true for mutations that confer NNRTI (non-nuke) resistance.

How long do mutations persist? The answer likely depends on the type and specifics of mutations. Some resistance substitutions(like the K103N) can persist at least for months, others might more readily revert to drug susceptible. We do know from several studies that the frequency of drug resistance mutations, even in the chronically infected persons is increasing-- suggesting to me that many mutations can persist in the absence of drug therapy.

For a practical issue, I've taken to doing baseline resistance testing (usually genotypes) in all treatment naive persons who present in the office for the first time (whether they are acutely or chronically infected). We've seen about 8-10% of these persons with some evidence of drug resistance-- a very frightening number.

Hope this helps, BY



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