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Terminology - resistance test

Nov 16, 2006

A physician mentioned to me the need for "the standard commercial resistance test"?

What test would this be exactly? (and what does it do)

Response from Dr. Wohl

What he or she means is a test to look at whether the virus has developed resistance to HIV medications.

There are two major types of HIV antiretroviral resistance tests. Both use virus from the patient's blood.

Genotype test: This test examines the genes of the HIV viruses collected from a blood sample and compares these genes to that of HIV known not to be resistant to any HIV meds. To become resistant to the HIV meds, the virus must mutate when reporducing, that is change some of its genes, so that offspring virus can survive despite the presence of the drugs. HIV mutates at specific genes for different HIV medications.

Phenotype test: Here the virus from a patient is grown in culture in a lab. The virus is subjected to different levels of HIV medicatications. If it takes a lot of medication to inhibit the virus from replicating, it is evidence that the virus is resistant to the effects of the drug.

Both tests are helpful. The genotype is usually performed quicker and is cheaper and therefore is more popular. If resistance is detected, then it generally indicates that the medication is not doing what we need it to do (and often it can also mean adherence has been suboptimal) and that a change is in order.

If that whet your appetite for more, check out:

Print out and read the best patient-focused info you will find on resistance and resistance test. Your MD will be most definitely impressed by your resistance savvy.


Just received lab results...very scared
Time to start meds????

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