Accurate quantifi cation of HIV-1 viral load (VL) is crucial for disease monitoring and management. This study was designed to compare HIV-1 VL determination between two of the major commercial real-time PCR-based methods, i.e., the Roche’s COBAS AmpliPrep/COBAS TaqMan HIV-1 Test and the Abbott Real Time HIV-1 Assay. Out of 308 paired plasma tested, 85.1% (262/308) of test results were concordant with 173 samples were quantifi able for VL and 89 were “Not Detected” (ND). There was a strong overall correlation of the quantifi able VL between the two methods (R2 =0.952). Comparison of the mean VL with differences of the two methods using the Bland Altman plot showed rough symmetric distribution of the differences, indicating neither method is better than the other for measuring VL. However, a relative high 14.9% (46/308) of discordant results was found between the two methods. χ2 test of those discordant results indicated a signifi cant difference (χ2= 96.37; p = <0.001). Of the 104 ND Roche samples, 15 (14.4%) were detected by Abbott method; of the 120 ND Abbott samples, 31 (25.8%) were detected by Roche method. Differences in gene target, test sensitivity, input volume and their abilities to detect different HIV-1 subtypes could potentially explain some of the discordance.

Accurate quantification of HIV-1 Viral Load (VL) in plasma compartment is crucial for disease monitoring and management (Braun et al., 2007; Ciotti et al., 2008). This method has now become a standard method for monitoring HIV-infected patients on antiretroviral therapy in the United States. This trend has lead to the development and approval of a number of diagnostic assays (For reviews of these assays, see Constantine and Zhao, 2005). There are currently two major commercial and FDA-approved real-time PCRbased methods, i.e., the Cobas AmpliPrep/Cobas TaqMan HIV-1 test (the Roche method; Roche Molecular Systems, Inc., Branchburg, NJ) and the Abbott Real Time HIV-1 assay (the Abbott method; Abbott Molecular Inc., Des Plaines, IL). These two assays share three common features 1) Additional reduction in the lower limits of detection (LOD) of HIV-1 RNA from the earlier version; 2) New primers and probes designs for recognition of the different viral subtypes and circulating recombinant forms (CRFs); and 3) Reduction in hand-on time by configuring the test near to full automation. Table 1 summarizes the assay characteristics of these two assays. Another common feature of these two assays is the use of realtime PCR as their underlying technology for the measurement of HIV1 viral load. Real-time PCR, also known as the TaqMan technology or 5’exonuclease assay, quantifies PCR products cycle-by-cycle (“realtime”) as they accumulate (Holland et al., 1991). This gene-target based amplification method is based on the determination of the threshold cycle (CT) when the amplified product is detected for the first time and the PCR is still in its exponential phase (Ciotti et al., 2008; Gibson et al., 1996; Gordillo et al., 2005; Scott et al., 2009). Different from the conventional PCR, an internal probe is added to the detection process, which is an oligo nucleotide with both a fluorescent reporter and a fluorescent quencher dye attached. If a target sequence is present, the probe anneals between the forward and reverse primers and is then digested by the 5’ nuclease activity of the DNA polymerase as PCR proceeds. Digestion of the probe DNA separates the reporter dye from the quencher dye, making the reporter dye signal detectable. Detection of the resulting fluorescence collectively provides an immediate real-time quantification of the PCR process.

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Robert Har