691 - Results of Repeat HIV-1 DNA Resistance Tests Are Highly Concordant

Background: DHHS guidelines recommend caution when interpreting HIV-1 DNA resistance testing because not all previously identified drug resistance mutations (DRMs) may be captured. Comparison of multiple reports from the same patient was performed to assess the ability of HIV-1 DNA testing to consistently identify wild-type and drug resistance alleles.

Methods: Patients with 3 HIV-1 DNA resistance tests (trios) and corresponding HIV-1 viral load (VL) measurements within ~3 months of each resistance test were identified in a commercial database. Concordance among trio test results was assessed for each patient. VL and trio timespan were evaluated for impact on concordance using one-way ANOVA with post-hoc analyses.

Results: Fifty-five patients with test trios were identified for analysis. Average patient age was 53 years, and 88% were male. All 3 tests within 26/55 trios were associated with VL< 200 copies/mL. The average testing timespan was 100 weeks (range 17-228 weeks). Wild-type virus was identified on 3/3 reports for 11/55 (20%) patients.  Among resistant viruses, DRMs were identified on average 70%, 20% and 10% on 3/3, 2/3 and 1/3 of HIV-1 DNA reports, respectively. M184V was identified on 3/3, 2/3 and 1/3 reports among 14/17, 2/17, and 1/17 test trios, respectively. K103N was identified on 3/3 and 2/3 reports among 11/12 and 1/12 test trios, respectively. The redetection rate following an initial HIV-1 DNA test was high for M184V (30/34, 88%) and K103N (23/24, 96%).
Of 178 DRMs detected across all initial HIV-1 DNA tests, 17 (9.6%) were not detected on the second, but redetected on the third test, including M184V and K103N in one trio each. The average concordance among test trios across all drug classes was 97%. No correlation between VL at time of testing and DRM redetection rates was observed. Significantly fewer DRMs were recaptured when repeat testing was performed > 24 months after the initial test.

Conclusion: Repeat HIV-1 DNA drug resistance testing reliably detected archived DRMs. DRM decay related to turnover of the viral reservoir may explain some discordance between repeat HIV-1 DNA tests.