More mutations will occur, and some of them could cause resistance. If you have to stop taking any antiviral medication, talk to your doctor about how to stop. You may have to stop some drugs sooner than others. If you are not taking any antiviral drugs, the wild type virus will multiply faster than any resistant mutations. Your medications should continue working for you.
Laboratory tests can measure phenotypic and genotypic resistance.
A sample of HIV is grown in the laboratory. A normal dose of one antiviral medication is added. The growth rate of the HIV is compared to the rate of wild type virus. If the sample grows more than normal, it is resistant to the medication. It can take over a month to get the results.