Evaluation of Hologic Aptima HIV-1 Quant Dx Assay on the Panther System on HIV Subtypes

Abstract

Quantitation of the HIV-1 viral load in plasma is the current standard of care for clinical monitoring of HIV-infected individuals undergoing antiretroviral therapy. This study evaluated the analytical and clinical performances of the Aptima HIV-1 Quant Dx assay (Hologic, San Diego, CA) for monitoring viral load by using 277 well-characterized subtype samples, including 171 cultured virus isolates and 106 plasma samples from 35 countries, representing all major HIV subtypes, recombinants, and circulating recombinant forms (CRFs) currently in circulation worldwide. Linearity of the Aptima assay was tested on each of 6 major HIV-1 subtypes (A, B, C, D, CRF01_AE, and CRF02_AG) and demonstrated an R(2) value of ≥0.996. The performance of the Aptima assay was also compared to those of the Roche COBAS AmpliPrep/COBAS TaqMan HIV-1 v.2 (CAP/CTM) and Abbott m2000 RealTime HIV-1 (RealTime) assays on all subtype samples. The Aptima assay values averaged 0.21 log higher than the CAP/CTM values and 0.30 log higher than the RealTime values, and the values were >0.4 log higher than CAP/CTM values for subtypes F and G and than RealTime values for subtypes C, F, and G and CRF02_AG. Two samples demonstrated results with >1-log differences from RealTime results. When the data were adjusted by the average difference, 94.9% and 87.0% of Aptima results fell within 0.5 log of the CAP/CTM and RealTime results, respectively. The linearity and accuracy of the Aptima assay in correctly quantitating all major HIV-1 subtypes, coupled with the completely automated format and high throughput of the Panther system, make this system well suited for reliable measurement of viral load in the clinical laboratory.

FIG 1

Linearity of Aptima results by HIV subtype. One representative of each subtype (A, B, C, D, CRF01_AE, and CRF02_AG), at dilutions ranging from 100 to 1,000,000 (log 2.0 to 6.0) copies/ml, was tested in duplicate in the Aptima assay. The average viral load for 2 replicates is plotted for each data point. Input copies are based on RealTime results.

FIG 2

Comparison of three assays on all viral subtypes tested. The results of RealTime, CAP/CTM, and Aptima testing of the 277 subtype samples tested are plotted against consensus values representing the means for the 3 measurements. The black solid and dotted lines represent the consensus ± 0.5 log. The green, blue, and red lines represent trend lines for the Aptima, CAP/CTM, and RealTime assays, respectively.

FIG 3

Bland-Altman analyses of Aptima versus CAP/CTM and RealTime quantitation of the subtype panel. Each point represents a separate sample. The central lines represent the biases of 0.214 (95% CI, 0.708 to −0.280) and 0.305 (95% CI, 0.790 to −0.180) for the CAP/CTM and RealTime assays, respectively.

FIG 4

Comparison of Aptima quantitative results versus CAP/CTM (red) and RealTime (blue) results by subtype. The difference between Aptima and CAP/CTM results (blue) or Aptima and RealTime results (red) is plotted by subtype, with each dot representing a single sample. The first column shows whisker plots for all the samples, indicating the means (center lines), 25th to 75th percentiles (boxes), and extents of outliers (lines). The solid black horizontal line represents the value for the Aptima assay (no difference), with the blue and red lines representing the average overall differences from the Aptima results of 0.21 log for the CAP/CTM assay and 0.30 log for the RealTime assay.