Abstract
We investigated the independent effects of HIV-1 ”target not detected” measurements versus those that were detectable but below the limit of quantification by Taqman RT-PCR assay on subsequent viral rebound as there are conflicting data regarding the clinical implications of arbitrary or isolated low-level viremia. Cox proportional hazard regression modeling was used to investigate the independent effects of the first HIV-1 load measurement after introduction of the Taqman RT-PCR assay (time-point 0 [T0]), pre-T0 viral loads, CD4 T cell count, race/ethnicity, gender, age and NNRTI use on risk of a confirmed VL >50, >200, >400 and >1000 copies/mL at 22 months follow-up in analyses of all patients and propensity-matched baseline cohorts. 778 patients had a viral load that was either not detected by RT-PCR (N = 596) or detectable, but below the limit of quantification (N = 182) at T0. Detectable viremia, lower T0 CD4 count, decreased age, and having detectable or unknown VL within a year prior to T0 were each associated with viral rebound to >50, >200 and >400 copies/mL. Overall failure rates were low and <5.5% of all patients had confirmed VL >1000 copies/mL. A majority of patients with rebound >200 copies/mL subsequently re-suppressed (28 of 53). A detectable VL <48 copies/mL was independently and significantly associated with subsequent viral rebound, and is cause for clinical concern.
Highlights
Monitoring the response to antiretroviral therapy relies upon measurements of HIV-1 RNA, with the goal to achieve virologic suppression, defined as a level below the limit of detection of the assay [1]
We investigated the independent effects of ’’target not detected’’ measurements versus those that were detectable but below the limit of quantification using the Roche Cobas Taqman RT-PCR assay on risk of virologic rebound in patients followed at two academic medical centers, and described virologic outcomes of patients experiencing rebound
Patients included in the analysis were selected based on the Taqman assay result at T0: those with viral loads (VL) that was detectable but below the limit of quantification (,48 copies/mL; BLQ), and those with VL reported as target not detected (TND)
Summary
Monitoring the response to antiretroviral therapy relies upon measurements of HIV-1 RNA, with the goal to achieve virologic suppression, defined as a level below the limit of detection of the assay [1]. As assays have become more sensitive, the frequency of detectable HIV-1 RNA at low levels and below the quantifiable range of these tests has become more common but the clinical significance of such results is unclear [2,3,4,5,6,7]. Data regarding the clinical implications of a detectable plasma HIV-1 RNA below the quantifiable limit of 50 copies/mL (very low-level viremia, VLLV) are mixed. Two studies have shown a significant association between sporadic VLLV measurements and viral rebound to above 50 or 400 copies/mL [8,9]. The methods for quantifying viral loads (VL) differed between these studies, and confounding may have been introduced, as patient characteristics, such as CD4 T cell counts, time of prior virologic control and the use of NNRTI-based regimens differed between baseline comparator groups [8,10,11]
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