The usual recommendation is a 2-week allowance. Interpretation of results in patients who have received prior antiretroviral agents is difficult. Resistance to previously used drugs may be present even if resistance assays indicate susceptibility, so that prior drug history and outcome are important factors in regimen selection. Results are most accurate with failure of early regimens. These are compared in Table 2-3.
Interpretation requires knowledge of mutational changes, eg, expertise.
Technician experience influences results. Assesses total effect, including mutations, mutational interactions. Reproducibility is good. Assays vary considerably based on cost, the number of mutations tested, and simplicity and accuracy of reporting. The table indicates the amino acids and corresponding letter codes used to describe mutations in genotype analyses.