Virco establishes comprehensive set of clinical cutoffs for the vircoŽTYPE HIV-1 resistance test


-- Research presented at ICAAC demonstrates value of clinical cutoffs in evaluating HIV drug resistance information --

Washington, D.C., October 31, 2004 – Investigators from Virco today presented data that establishes a comprehensive set of clinical cutoffs -- a newly established threshold for optimal selection and evaluation of antiretroviral regimens -- for the virco®TYPE HIV-1 resistance test. These reference values are derived from the largest clinical outcomes database used to generate clinical cutoffs, and apply a consistent and clinically relevant approach to help physicians better evaluate HIV drug resistance information. These clinical cutoffs are available for a wider range of antiretroviral drugs than those offered by other HIV resistance tests.

In her presentation today at the 44th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), Lee Bacheler, PhD, vice president, Clinical Virology, at Virco, demonstrated how clinical cutoffs for the virco®TYPE HIV-1 assay, based on a large and high-quality outcomes database that incorporates more than 3,000 therapeutic regimens, provide physicians with clinically relevant resistance information. She and her colleagues employed virco®TYPE analysis of viral genotypes to predict quantitative phenotypic resistance levels. Mathematical models of virologic response to antiretroviral drugs at eight and 24 weeks versus baseline fold change in IC50 (concentrations of drugs that inhibit 50% of viral replication) were constructed using linear regression. Clinical cutoffs (CCOs) were defined as virco®TYPE-predicted fold change values for 20% and 80% loss of viral load response.

"Our study supports the value of clinical cutoffs in facilitating rational selection of antiretroviral treatment," commented Dr. Bacheler. "The clinical cutoffs enhance the value of the virco®TYPE HIV-1 test by applying consistent definitions across antiretroviral drugs. The results are more closely related to actual treatment practices, with the potential to improve medical management of people with HIV."

Dr. Bacheler reported that baseline fold change (FC) values associated with a modest reduction (20%) in the eight-week viral load response were low, whereas baseline fold change values associated with a more substantial (80%) loss of viral load response were often quite high. However, in both cases, these FC values were higher than those derived from wild-type clinical isolates

Clinical cutoff ranges: clinical response at eight weeks1

20% reduction of wild type response 80% reduction of wild type response
boosted* PIs 0.9 to 10 FC 6.5 to 62 FC
unboosted protease inhibitors (PIs) 0.7 to 1.0 FC 1.0 to 2.2 FC
FC values of wild type clinical isolates 0.6 to 0.9

CCOs based on 24-week outcome data were similar, Dr. Bacheler observed.1 A summary of her ICAAC presentation, including the CCO values, will be available for download at

"The predictive value of the virco®TYPE analysis, through the use of clinical cutoffs, has profound implications for the practicing physician," commented Calvin J. Cohen, MD, MSc, of the Community Research Initiative of New England. "These data are critical to helping physicians optimize treatment regimens, as they provide valuable insight into how to interpret a resistance test."

Advantages of the virco®TYPE HIV-1 Test

The virco®TYPE HIV-1 test is the first resistance test that provides phenotypic information and expert clinical knowledge at a fraction of the cost of conventional phenotyping, and the only resistance test to which consistent CCOs can be applied. Compared to biological cutoffs, CCOs represent a different, more clinically relevant approach to interpreting resistance information, providing a higher degree of correlation with virologic outcomes. Additionally, unlike the approach for biologic cutoffs, the approach used to determine CCOs considers the effects of drugs used in combination regimens.

The virco®TYPE HIV-1 report reflects genotypic and phenotypic analysis, informed by Virco's proprietary Expert Clinical Knowledge. The test yields rapid, cost-effective results within 48 hours.

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Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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