Understanding RT

What is resistance testing?

HIV drug resistance testing can determine what anti-retroviral drugs will be more, or less effective against your specific HIV virus. There are three main types of HIV drug resistance testing: genotyping, phenotyping and virtual phenotyping.

Genotyping: Genotypic tests read the genetic code of the virus to detect mutations or differences from "wild-type" or "normal" HIV. Based on the pattern of these mutations and a set of rules put together by a panel of experts, your doctor can predict which drugs your virus will be resistant to and which it will be susceptible to (ie which drugs will work against your virus). You can think of genotyping as a "qualitative" prediction of resistance and susceptibility.

Phenotyping: Phenotypic tests are a direct measure of resistance. In the laboratory, a technician measures the ability of the virus to grow in the presence of different concentrations of each of the available drugs. Resistant viruses are able to grow in higher concentrations of drug than susceptible viruses. You can think of phenotyping as a "quantitatative" prediction of resistance and susceptibility. Virco's Antivirogram® has been shown to predict clinical outcome in prospective clinical trials.

VirtualPhenotyping: virco® TYPE HIV-1 provides the best of both worlds, ie it is a combination of genotyping and prediction of phenotype. So, in addition to your doctor knowing the mutation pattern of your virus, (s)he gets a quantitative measure of the degree of resistance or susceptibility of your virus for each particular drug. For more information about the virco® TYPE HIV-1, please consult the vircoTYPE HIV-1 section.
 

When do I need a Resistance Test?

While there is still debate as to when a resistance test is needed, a number of international and national organizations have drawn up guidelines on this important question. Some of these guidelines recommend that testing be performed when a patient is first diagnosed with an HIV infection or before an infected patient begin their first treatment. Most of the guidelines agree that it is important to do resistance testing the first time treatment fails, if more than one treatment regimen fails and when a patient is pregnant.

More and more newly diagnosed patients have viruses that are already resistant to some of the available drugs. This is one reason to perform a resistance test before beginning antiretroviral treatment.

For more information on resistance testing guidelines, please consult the Guidelines section.
 

How do I get a Resistance Test?

Virco provides a number of different ways for your physician to order a Virco resistance analysis.

This can be done either by providing a blood sample if you would like to have a new test, or by providing a report of your viral RNA sequence for any resistance test already carried out or about to be carried out for you.

Speak with your doctor to determine if a Virco resistance test is right for you.