Generally speaking, there are two types of drug-resistance tests available to HIV-positive patients: genotypic and phenotypic assays. Because genotypic testing provides results in one to two weeks—compared to the two-, three- or four-week turnaround associated with phenotypic testing—it is the preferred choice for patients who have yet to start treatment.
Among patients who have used multiple drugs in the past, interpreting the results of both tests together may be most useful. One company, Monogram Biosciences, will phenotype and genotype a blood sample and provide the results of both tests on the same lab report—called PhenoSense GT.
The next two sections review genotypic and phenotypic tests in detail.
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