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Drug Resistance Testing
Apr 3, 2002

I tested positive 2 weeks ago and have been trying to absorb as much of the information that's available. My first lab results showed my viral load at 7595, my CD4 at 547, and my CD8(?) at 1274. My physician recommended that I not start treatment right away. I have to go back in six weeks to get blood drawn again. I am currently with a family practice physician and am researching HIV specialists in the area. I was not offered drug resistance testing nor was it mentioned. I am going to request that it be done. Would it be a good idea to get it done before my next visit in 6 weeks? I read it can take 14 days to get the results back. I don't want to go to my next visit and find out I need to start treatment and have to wait 2 more weeks. I am not sure if there is a timeframe involved that I should worry about. Also, I am leaning toward the phenotypic testing. What would determine if genotypic vs. phenotypic testing should be done? Thank you for your time.

Response from Dr. Little

I am generally of the opinion that a pre-treatment drug resistance test is a good idea among newly diagnosed individuals. There is very good data now to suggest that this is a good idea in recently infected individuals, and less data to address whether this is still worth the cost in chronically infected (ie more than 1 year infected) people. It is often quite difficult to estimate how long you have been infected, but if you and your doctor think that you may have contracted HIV during the last 3-5 years, then I think that HIV drug resistance testing is quite reasonable. This is not currently the recommended standard of care - hence many non-HIV and even many HIV experts do not agree with this approach. My general feeling is that while a negative test (ie no resistance) does not exclude the possiblity of some level of drug resistance (below the limit of detection of the study), a positive test (ie identified drug resistance), can be extremely helpful in guiding treatment decisions.

In terms of whether to delay the start of therapy while waiting on these test results, this comes down to how long you have been infected and how likely you think you it is that the person who infected you may have taken antiretroviral therapy. This is a difficult question, and not one I can answer without more information.

In terms of which test to have done (genotype or phenotype) - I think this depend upon which test your care provider has more experience interpreting. I think that as a pretreatment screen, you often get more information from a genotype test, but this test is also more difficult to interpret if you are not used to reading these test results. The phenotype test can be used in the event that your care provider is not familiar with drug resistance and HIV. Alternatively, get a genotype, and ask for an interpretation from someone who is familiar with drug resitance test results. Hope this helps.

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