Response to Waters et al. ‘Successful use of genotypic resistance testing in HIV-1-infected individuals with detectable viraemia …’

Abstract

Waters et al. [1] recently reported their success of 69.4–92.9% in HIV genotypic resistance antiretroviral testing for clinical samples with low viremia (between 50 and 1000 copies/ml) using the ABI 3730XL sequencer and Virco BVBA proprietary primer mixers (Mechelen, Belgium). Their lowest rate of amplification and sequencing was at the HIV-RNA range of 50–200 copies/ml. We had also obtained credible genotypic resistance results from low viral loads and performed validation of the commercial HIV genotypic resistance kit, TruGene (Bayer HealthCare, Tarrytown, New York, USA), in our laboratory. In a comparison of original clinical plasma specimens with samples diluted to approximately 100 copies/ml, we found that resistance interpretations were 97.1% concordant, and our testing performance was not significantly affected, as measured by multiple assay parameters [2]. Subsequently, our laboratory accepted clinical samples from untreated patients whose viral loads were 400 copies/ml or greater, patients whose HIV RNA did not achieve less than 400 copies/ml by 24 weeks or less than 75 copies/ml by 48 weeks of treatment, or treated patients whose viral loads rebounded above those levels on two occasions. Using these criteria, 39 out of 389 of our genotypic resistance testing samples (10%) were less than 1000 copies/ml. A rate of 92.3% for successful amplification and sequencing was identical for both HIV-RNA ranges of 75–399 copies/ml (12/13) and 400–999 copies/ml (24/26). By comparison, the remaining 350 clinical samples with HIV RNA of 1000 copies/ml or greater had successful amplification and sequencing at a rate of 98.6%. The clinical goal of antiretroviral therapy is durable and maximal viral suppression [3], as circulating viremia has been shown to be a compelling prognosticator of HIV progression [4]. Therefore, the importance of detecting drug resistance with low HIV viremia is paramount, because a timely therapeutic change would spare the continuation of a failing regimen and prevent the development of untoward drug interactions and toxicities. We agree with Waters et al. [1] that laboratories should explore genotypic resistance testing on clinical samples with HIV RNA of less than 1000 copies/ml. However, we caution that each laboratory should establish the performance characteristics of its method before routine genotypic resistance testing for samples with low viremia. Disclaimer: The views expressed in this letter are those of the authors and do not necessarily represent the views of the Department of Veterans Affairs.