Description of Procedure or Service
- Description
Human immunodeficiency virus (HIV) is an RNA retrovirus that infects human immune cells (specifically CD4 cells) causing progressive deterioration of the immune system ultimately leading to acquired immune deficiency syndrome (AIDS) characterized by susceptibility to opportunistic infections and HIV-related cancers (CDC, 2014). - Literature Review
The HIV virus replicates rapidly, with a replication cycle rate of approximately 1 day in which more than 109 virions can be produced(J. Coffin & Swanstrom, 2013; Ho et al., 1995). Furthermore, reverse transcriptase is error-prone, the overall single-step point mutation rate for HIV-1 is ∼3 × 10−5 mutations per base per replication cycle(Mansky & Temin, 1995) leading to approximately one genome in three containing a mutation after each round of replication, some of which confer drug resistance(J. M. Coffin, 1995). This rate is about average for an RNA virus and that it is the pace of replication, the duration of infection, and the size of the replicating population, allowing it to evolve rapidly in response to selective influences (J. Coffin & Swanstrom, 2013).
Drug-resistant variants, which generally replicate slower than wild type, can pre-exist at low levels before drug therapy is initiated and emerge to cause overt virologic failure, or become more drug resistant by the gradual accumulation of additional resistance mutations (Kozal, 2017a, 2017b).
Drug resistant HIV variants can be assessed using phenotypic testing and genotypic testing. Both assays are limited by their decreased sensitivity for low-level minority variants that comprise less than 5 to 20 percent of the virus population(Kozal, 2017b).
Genotypic assays detect the presence of specific drug resistance mutations in the protease, reverse transcriptase, and integrase genes. Advantages include lower cost and shorter turnaround time, however are complicated by difficulty in interpretation when many mutations as combinations of individual mutations may have a differential effect on resistance that differs from the individual mutation alone(Kozal, 2017b). Mutations are known to cause resistance to certain drugs, but increase susceptibility to others, impact viral fitness and contribute to major pathways of resistance and the interactions of mutations effecting various mechanisms can be difficult to predict, over 20 rules-based genotypic interpretation systems (GIS) have been proposed(Fox et al., 2007; Kozal, 2017b).
Phenotypic resistance assays measure the extent to which an antiretroviral drug inhibits virus replication. The major advantages of phenotypic testing is the direct measure of drug susceptibility. Limitations include a longer turnaround time, expense, and biologic cut-offs above achievable drug levels. Phenotypic resistance assays may be helpful when evaluating HIV strains with known or suspected complex drug resistance mutation patterns as their actual resistance may not be accurately predicted by simply detecting the presence of multiple mutations(Kozal, 2017b).
Antiretroviral therapy guided by genotypic and phenotypic susceptibility testing leads to better viral suppression(Baxter et al., 2000) and has been associated with improved survival(Palella et al., 2009). The emergence of drug resistance may also affect the rate of immunologic recovery(Trotta et al., 2010).The use of drug resistance testing further supported by a study of its cost effectiveness in a hypothetical cohort of antiretroviral-naïve patients(Sax et al., 2005). - Applicable Federal Regulations
On September 26, 2001 FDA approved Visible Genetics, Inc., TrueGene HIV-1 Genotyping Kit and Open Gene DNA Sequencing System to be used to identify drug resistance in HIV patients.
On November 26, 2002 the FDA approved the Roche Molecular Systems, Ic Cobas Ampliscreen System.
On September 5, 2013 the FDA approved Celera Corporation’s ViroSeq HIV Genotyping System v2.0.
***Note: This Medical Policy is complex and technical. For questions concerning the technical language and/or specific clinical indications for its use, please consult your physician.