According to research reported at the 16th Conference on Retroviruses and Opportunistic Infections (CROI), the genetically divergent strains of the HIV virus became increasingly prevalent in the US. The ability of clinicians to effectively monitor the progress of anti-viral drug therapies depends on the capacity of viral load assays to accurately quantitate, or measure these variant HIV strains. A study by the Global HIV Surveillance Program at Abbott showed significant variation in the ability of diagnostic tests to accurately monitor viral load in patients infected with differing strains, or subtypes, of the HIV virus. The study evaluated HIV-infected specimens using the Abbott RealTime HIV-1 test and the Roche COBAS Taqman HIV-1 test. According to the study, the Abbott RealTime HIV assay quantitated HIV more accurately than the widely used COBAS Taqman assay in an analysis of 317 seropositive samples from seven countries: Argentina, Brazil, Cameroon, Saudi Arabia, South Africa, Thailand and Uganda. The samples included six different HIV subtypes and eight circulating recombinant forms. Only 18 samples were subtype B, the most common HIV strain in the US. The research showed the Taqman assay failed to detect five infected samples and underquantified viral load in 38 samples, compared to the Abbott assay. "The differences in viral load quantitation between assays is likely due to the impact of HIV genetic variation on assay performance," said John Hackett, Ph.D., lead author from the Abbott HIV Global Surveillance Program. "Since viral load measurement is critical for optimal patient management, clinicians must recognize that HIV diversity can influence the accuracy and reliability of assay performance." The Abbott RealTime HIV-1 test is used in conjunction with clinical presentation and other laboratory markers as an indicator of disease prognosis, and as an aid in assessing viral response to antiretroviral treatment as measured by changes in plasma HIV-1 RNA levels. The RealTime assay is not intended for use as a donor-screening test for HIV-1 or as a diagnostic test to confirm the presence of HIV-1 infection.