We read with interest the findings of Damond et al. (1) showing the lack of agreement between plasma viral load measurements performed by the Cobas Amplicor human immunodeficiency virus type 1 (HIV-1) Monitor test, version 1.5 (Roche Molecular Systems, Inc., Branchburg, NJ) and the Cobas AmpliPrep/Cobas TaqMan HIV-1 test (Roche Molecular Systems, Inc.). The authors found generally good overall agreement between the assays, with mean values of 2.99 and 2.51 log₁₀ copies/ml for the Cobas Amplicor HIV-1 Monitor test, version 1.5, and the Cobas AmpliPrep/Cobas TaqMan HIV-1 test, respectively, but substantial differences were noted between the results for some specimens. The reasons for the lack of result agreement in these specimens remain unclear.

Unfortunately, the authors included only a brief statement that routine clinical testing in their laboratory was performed with the Cobas Amplicor HIV-1 Monitor test, version 1.5, following automated nucleic acid extraction using a “MagNA Pure large-volume kit.” One wonders if the authors were referring specifically to the MagNA Pure LC instrument (Roche Diagnostics, Indianapolis, IN) and the MagNA Pure LC total nucleic acid isolation kit-large volume (Roche Diagnostics) and using them in conjunction with the Cobas Amplicor assay for (i) routine clinical testing and (ii) analyzing the 160 plasma specimens included in their study. These procedural details are unclear from the authors' description of their routine clinical testing and comparative study methods (1).

There are only two published papers describing the use of automated nucleic acid extraction methods utilizing the MagNA Pure LC instrument in conjunction with either the Cobas Amplicor HIV-1 Monitor test, version 1.5, or the Amplicor HIV-1 Monitor test, version 1.5 (2, 3). One wonders if Damond et al. have adopted or modified either of these methods for use with the Cobas Amplicor assay or validated their own method. Readers would benefit from the authors' provision of appropriate, specific literature references along with additional details of their specific methods used for performing the Cobas Amplicor assay. One can accurately interpret the study findings and conclusions only after being assured that the authors' modifications to the Cobas Amplicor assay procedure did not contribute to the significant discrepancies in HIV-1 RNA levels observed in this study. These procedural details are critical to understanding the implications of the authors' findings for diagnostic laboratories that are considering the use of the Cobas AmpliPrep/Cobas TaqMan HIV-1 test for routine clinical testing.

• Copyright © 2008 American Society for Microbiology