Comparison of the LCx Human Immunodeficiency Virus (HIV) RNA Quantitat
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《微生物临床杂志》
Division of Virology, Department of Infectious Diseases, Montpellier University Hospital, 34295 Montpellier, France
ABSTRACT
The LCx human immunodeficiency virus (HIV) RNA Quantitative, RealTime HIV, and COBAS AmpliPrep-COBAS TaqMan assays for HIV type 1 (HIV-1) were compared for their abilities to quantitate HIV-1 RNA in plasma. High degrees of correlation and agreement were observed between the assays. Differences in HIV-1 RNA levels according to HIV-1 subtypes did not reach statistical significance.
TEXT
Measurement of human immunodeficiency virus (HIV) type 1 (HIV-1) RNA levels in plasma is a major tool for the management of HIV-1-infected patients. Several commercial assays based on viral nucleic acid amplification have been developed over the course of the past decade. These different assays have been progressively improved by (i) lowering the lower limit of HIV-1 RNA detection and quantitation (6, 7, 9, 13), (ii) adapting primers and a probe for recognition of the different HIV-1 subtypes and circulating recombinant forms (CRFs) (5, 8, 12, 15-17), and (iii) developing automated methods (2, 11). More recently, commercial assays based on real-time nucleic acid amplification methods have been developed (4, 10). In the present study, we have compared the analytical performances of three assays: the LCx HIV RNA Quantitative assay (Abbott Molecular, Rungis, France), based on end-point PCR; the RealTime HIV assay (Abbott); and the COBAS AmpliPrep-COBAS TaqMan HIV-1 test (Roche Diagnostics, Meylan, France). The last two assays are based on real-time PCR. The Abbott LCx HIV RNA Quantitative and the RealTime HIV assays target the pol integrase region of HIV-1, whereas the COBAS AmpliPrep-COBAS TaqMan HIV-1 test targets the gag p24 region of HIV-1. Using the 1-ml sample preparation protocol, the reported upper limit of quantitation and lower limit of quantitation (LLQ) are 1,000,000 (6.0 log10) RNA copies/ml and 50 (1.7 log10) RNA copies/ml, respectively, for the LCx HIV RNA Quantitative assay, and 10,000,000 (7.0 log10) RNA copies/ml and 40 (1.6 log10) RNA copies/ml, respectively, for both the Abbott RealTime HIV-1 and the COBAS AmpliPrep-COBAS TaqMan HIV-1 test.
Plasma samples were obtained from 91 HIV-1-seropositive patients: 58 of them were infected with HIV-1 subtype B and 30 were infected with non-B subtypes (Table 1). For the remaining three patients, the HIV-1 subtype could not be determined because of an insufficient RNA level or a lack of sample availability.
Plasma samples were frozen at –80°C before testing. For the LCx HIV RNA Quantitative and the Abbott RealTime HIV assays, automatic RNA extraction was performed on an M1000 apparatus (Abbott) with the 1-ml sample preparation protocol and with elution volumes of 140 μl for the LCx HIV RNA Quantitative assay and 70 μl for the RealTime HIV assay. For the COBAS AmpliPrep-COBAS TaqMan HIV-1 test, extraction was done on an AmpliPrep apparatus (Roche Diagnostics) with 0.85 ml of plasma and an elution volume of 75 μl. The three assays were then performed by following the manufacturer's instructions and by using a 50-μl eluate volume. For calculations, the value of the LLQ was assigned to samples with HIV RNA levels below the LLQ.
HIV-1 RNA levels fell within the dynamic ranges of the three assays for 62 (68.1%) samples, whereas it was lower than the LLQ of the three assays for 14 (15.4%) samples and was lower than the LLQ of one or two of the three assays for the remaining 15 (16.5%) samples. Overall, the LCx HIV RNA Quantitative, RealTime HIV, and COBAS AmpliPrep-COBAS TaqMan HIV-1 assays allowed quantitation of HIV-1 RNA in 67 (73.6%), 70 (76.9%), and 70 (76.9%) of the samples, respectively. HIV-1 RNA was detected at a level lower than the LLQ in eight, four, and nine additional samples by the LCx HIV RNA Quantitative, RealTime HIV, and COBAS AmpliPrep-COBAS TaqMan HIV-1 assays, respectively. Thus, the number of samples positive for HIV-1 RNA were 75 (82.4%) with the LCx HIV RNA Quantitative assay, 74 (81.3%) with the RealTime HIV assay, and 79 (86.8%) with the COBAS AmpliPrep-COBAS TaqMan HIV-1 assay (P = 0.57).
As shown in Table 1, a significant difference in the number of samples with HIV-1 RNA levels higher than the LLQ was not observed between the assays. CRF02_AG HIV-1 RNA could be detected at a level lower than the LLQ in two, one, and three additional samples by the LCx HIV RNA Quantitative, RealTime HIV, and COBAS AmpliPrep-COBAS TaqMan HIV-1 assays, respectively. Thus, the number of samples positive for CRF02_AG HIV-1 RNA were 8 (72.7%) with the LCx HIV RNA Quantitative assay, 10 (90.9%) with the RealTime HIV assay, and 10 (90.9%) with the COBAS AmpliPrep-COBAS TaqMan HIV-1 assay (P = 0.58).
As shown in Table 2, the HIV-1 RNA levels measured by the RealTime HIV assay in samples from subtype B-infected patients were lower than those obtained by either the LCx HIV RNA quantitative assay or the COBAS AmpliPrep-COBAS TaqMan HIV-1 test. Conversely, the HIV-1 RNA levels measured with the RealTime HIV assay in samples from patients infected with CRF02_AG HIV-1 strains were higher than those obtained with the two other assays, but these differences were not statistically significant.
As shown in Fig. 1, a high level of correlation between assays was observed, with Pearson's correlation coefficient (r) values ranging from 0.94 to 0.98. The agreement between methods was analyzed by using Bland-Altman plot analysis (3), and high levels of agreement were observed: 93.4% between the LCx HIV RNA Quantitative and the RealTime HIV assays as well as between the LCx HIV RNA Quantitative and the COBAS AmpliPrep-COBAS TaqMan HIV-1 assays and 94.5% between the RealTime HIV and the COBAS AmpliPrep-COBAS TaqMan HIV-1 assays (Fig. 2).
Taken together these data indicate that the three assays have similar performances for the quantitation of HIV-1 RNA in the samples tested in this study. The Abbott RealTime HIV assay and the COBAS AmpliPrep-COBAS TaqMan HIV-1 assay, both of which are supported by a fully automated extraction and both of which are based on real-time PCR, allow high throughputs (48 to 96 samples) and short turnaround times (nearly 3 h). This could be a major advantage for clinical laboratories.
In several studies, it has been reported that the LCx HIV RNA Quantitative assay is effective for quantitation of HIV-1 RNA in plasma samples from subjects infected with various group M subtypes, including CRF02_AG (15), or with group O viruses (14, 17). However, in one study, it has been reported that the performance of this assay is suboptimal only for the detection and quantification of CRF02_AG HIV-1 RNA (1). In the present study, HIV-1 RNA could be quantitated in 6 of 11 (54.5%) CRF02_AG-infected samples by the LCx HIV RNA Quantitative assay, whereas HIV-1 RNA could be quantitated in 7 (63.6%) and 9 (81.8%) of these samples by the COBAS AmpliPrep-COBAS TaqMan HIV-1 assay and the RealTime HIV assay, respectively. It was also observed that the HIV-1 RNA levels measured by the RealTime HIV assay were higher than those measured by the two other assays in the CRF02_AG-infected samples but were lower than those measured by the other two assays in subtype B-infected samples. These differences, however, did not reach statistical significance. This lack of significance could be due to small sample sizes. Therefore, larger studies are needed to better assess the possible impact of HIV-1 genetic diversity on the HIV-1 RNA levels measured by these assays.
ACKNOWLEDGMENTS
We acknowledge Abbott Molecular and Roche Diagnostics for providing test kits.
FOOTNOTES
Corresponding author. Mailing address: Laboratoire de Virologie, Hpital Saint-Eloi, 80 Avenue Augustin Fliche, 34295 Montpellier Cedex 05, France. Phone: (33) 467 337 127. Fax: (33) 467 337 793. E-mail: m-segondy@chu-montpellier.fr.
REFERENCES
Amendola, A., L. Bordi, C. Angeletti, E. Girardi, G. Ippolito, and M. R. Capobianchi. 2004. Comparison of LCx with other current viral load assays for detecting and quantifying human immunodeficiency virus type 1 RNA in patients infected with the circulating recombinant form A/G (CRF02). J. Clin. Microbiol. 42:811-815.
Berger, A., L. Scherzed, M. Sturmer, W. Preiser, H. W. Doerr, and H. F. Rabenau. 2002. Evaluation of the Cobas AmpliPrep/Cobas Amplicor HIV-1 Monitor Ultrasensitive test: comparison with the Cobas Amplicor HIV-1 Monitor test (manual specimen preparation). J. Clin. Virol. 25(Suppl. 3):S103-S107.
Bland, J. M., and D. G. Altman. 1999. Measuring agreement in method comparison studies. Stat. Methods Med. Res. 8:135-160.
de Mendoza, C., M. Koppelman, B. Montes, V. Ferre, V. Soriano, H. Cuypers, M. Segondy, and T. Oosterlaken. 2005. Multicenter evaluation of the Nuclisens EasyQ HIV-1 v1.1 assay for the quantitative detection of HIV-1 RNA in plasma. J. Virol. Methods 127:54-59.
Elbeik, T., W. G. Alvord, R. Trichavaroj, M. de Souza, R. Dewar, A. Brown, D. Chernoff, N. L. Michael, P. Nassos, K. Hadley, and V. L. Ng. 2002. Comparative analysis of HIV-1 viral load assays on subtype quantification: Bayer Versant HIV-1 RNA 3.0 versus Roche Amplicor HIV-1 Monitor version 1.5. J. Acquir. Immune Defic. Syndr. 29:330-339.
Erali, M., and D. R. Hillyard. 1999. Evaluation of the ultrasensitive Roche Amplicor HIV-1 MONITOR assay for quantitation of human immunodeficiency virus type 1 RNA. J. Clin. Microbiol. 37:792-795.
Erice, A., D. Brambilla, J. Bremer, J. B. Jackson, R. Kokka, B. Yen-Lieberman, and R. W. Coombs. 2000. Performance characteristics of the QUANTIPLEX HIV-1 RNA 3.0 assay for detection and quantitation of human immunodeficiency virus type 1 RNA in plasma. J. Clin. Microbiol. 38:2837-2845.
Holguin, A., B. Aracil, A. Alvarez, C. Barros, and V. Soriano. 2001. Prevalence of human immunodeficiency virus type 1 (HIV-1) non-B subtypes in foreigners living in Madrid, Spain, and comparison of the performances of the AMPLICOR HIV-1 MONITOR version 1.0 and the new automated version 1.5. J. Clin. Microbiol. 39:1850-1854.
Johanson, J., K. Abravaya, W. Caminiti, D. Erickson, R. Flanders, G. Leckie, E. Marshall, C. Mullen, Y. Ohhashi, R. Perry, J. Ricci, J. Salituro, A. Smith, N. Tang, M. Vi, and J. Robinson. 2001. A new ultrasensitive assay for quantitation of HIV-1 RNA in plasma. J. Virol. Methods 95:81-92.
Katsoulidou, A., M. Petrodaskalaki, V. Sypsa, E. Papachristou, C. G. Anastassopoulou, P. Gargalianos, A. Karafoulidou, M. Lazanas, T. Kordossis, A. Andoniadou, and A. Hatzakis. 2006. Evaluation of the clinical sensitivity for the quantification of human immunodeficiency virus type 1 RNA in plasma: comparison of the new COBAS TaqMan HIV-1 with three current HIV-RNA assays—LCx HIV RNA quantitative, Versant HIV-1 RNA 3.0 (bDNA) and COBAS AMPLICOR HIV-1 Monitor v1.5. J. Virol. Methods 131:168-174.
Muller, Z., E. Stelzl, M. Bozic, J. Haas, E. Marth, and H. H. Kessler. 2004. Evaluation of automated sample preparation and quantitative PCR LCx assay for determination of human immunodeficiency virus type 1 RNA. J. Clin. Microbiol. 42:1439-1443.
Parekh, B., S. Phillips, T. C. Granade, J. Baggs, D. J. Hu, and R. Respess. 1999. Impact of HIV type 1 subtype variation on viral RNA quantitation. AIDS Res. Hum. Retrovir. 15:133-142.
Segondy, M., T. D. Ly, M. Lapeyre, and B. Montes. 1998. Evaluation of the Nuclisens HIV-1 QT assay for quantitation of human immunodeficiency virus type 1 RNA in plasma. J. Clin. Microbiol. 36:3372-3374.
Swanson, P., B. J. Harris, V. Holzmayer, S. G. Devare, G. Schochetman, and J. Hackett. 2000. Quantification of HIV-1 group M (subtypes A-G) and group O by the LCx HIV RNA quantitative assay. J. Virol. Methods 89:97-108.
Swanson, P., C. de Mendoza, Y. Joshi, A. Golden, R. L. Hodinka, V. Soriano, S. G. Deware, and J. Hackett. 2005. Impact of human immunodeficiency virus type 1 (HIV-1) genetic diversity on performance of four commercial viral load assays: LCx HIV RNA Quantitative, AMPLICOR HIV-1 MONITOR v1.5, VERSANT HIV RNA 3.0, and NucliSens HIV-1 QT. J. Clin. Microbiol. 43:3860-3868.
Triques, K., J. Coste, J. L. Perret, C. Segarra, E. Mpoudi, J. Reynes, E. Delaporte, A. Butcher, K. Dreyer, S. Herman, J. Spadoro, and M. Peeters. 1999. Efficiencies of four versions of the AMPLICOR HIV-1 MONITOR test for quantification of different subtypes of human immunodeficiency virus type 1. J. Clin. Microbiol. 37:110-116.
Troonen, H., H. Grey, and G. Michel. 2002. Multicenter study of the LCx HIV RNA quantitative assay—a new competitive reverse transcriptase-PCR which targets pol genomic region of HIV-1 for the measurement of type B, non-type B and group O HIV-1 RNA. Clin. Chem. Lab. Med. 40:698-704.(Vincent Foulongne, Brigitte Montes, Mari)
ABSTRACT
The LCx human immunodeficiency virus (HIV) RNA Quantitative, RealTime HIV, and COBAS AmpliPrep-COBAS TaqMan assays for HIV type 1 (HIV-1) were compared for their abilities to quantitate HIV-1 RNA in plasma. High degrees of correlation and agreement were observed between the assays. Differences in HIV-1 RNA levels according to HIV-1 subtypes did not reach statistical significance.
TEXT
Measurement of human immunodeficiency virus (HIV) type 1 (HIV-1) RNA levels in plasma is a major tool for the management of HIV-1-infected patients. Several commercial assays based on viral nucleic acid amplification have been developed over the course of the past decade. These different assays have been progressively improved by (i) lowering the lower limit of HIV-1 RNA detection and quantitation (6, 7, 9, 13), (ii) adapting primers and a probe for recognition of the different HIV-1 subtypes and circulating recombinant forms (CRFs) (5, 8, 12, 15-17), and (iii) developing automated methods (2, 11). More recently, commercial assays based on real-time nucleic acid amplification methods have been developed (4, 10). In the present study, we have compared the analytical performances of three assays: the LCx HIV RNA Quantitative assay (Abbott Molecular, Rungis, France), based on end-point PCR; the RealTime HIV assay (Abbott); and the COBAS AmpliPrep-COBAS TaqMan HIV-1 test (Roche Diagnostics, Meylan, France). The last two assays are based on real-time PCR. The Abbott LCx HIV RNA Quantitative and the RealTime HIV assays target the pol integrase region of HIV-1, whereas the COBAS AmpliPrep-COBAS TaqMan HIV-1 test targets the gag p24 region of HIV-1. Using the 1-ml sample preparation protocol, the reported upper limit of quantitation and lower limit of quantitation (LLQ) are 1,000,000 (6.0 log10) RNA copies/ml and 50 (1.7 log10) RNA copies/ml, respectively, for the LCx HIV RNA Quantitative assay, and 10,000,000 (7.0 log10) RNA copies/ml and 40 (1.6 log10) RNA copies/ml, respectively, for both the Abbott RealTime HIV-1 and the COBAS AmpliPrep-COBAS TaqMan HIV-1 test.
Plasma samples were obtained from 91 HIV-1-seropositive patients: 58 of them were infected with HIV-1 subtype B and 30 were infected with non-B subtypes (Table 1). For the remaining three patients, the HIV-1 subtype could not be determined because of an insufficient RNA level or a lack of sample availability.
Plasma samples were frozen at –80°C before testing. For the LCx HIV RNA Quantitative and the Abbott RealTime HIV assays, automatic RNA extraction was performed on an M1000 apparatus (Abbott) with the 1-ml sample preparation protocol and with elution volumes of 140 μl for the LCx HIV RNA Quantitative assay and 70 μl for the RealTime HIV assay. For the COBAS AmpliPrep-COBAS TaqMan HIV-1 test, extraction was done on an AmpliPrep apparatus (Roche Diagnostics) with 0.85 ml of plasma and an elution volume of 75 μl. The three assays were then performed by following the manufacturer's instructions and by using a 50-μl eluate volume. For calculations, the value of the LLQ was assigned to samples with HIV RNA levels below the LLQ.
HIV-1 RNA levels fell within the dynamic ranges of the three assays for 62 (68.1%) samples, whereas it was lower than the LLQ of the three assays for 14 (15.4%) samples and was lower than the LLQ of one or two of the three assays for the remaining 15 (16.5%) samples. Overall, the LCx HIV RNA Quantitative, RealTime HIV, and COBAS AmpliPrep-COBAS TaqMan HIV-1 assays allowed quantitation of HIV-1 RNA in 67 (73.6%), 70 (76.9%), and 70 (76.9%) of the samples, respectively. HIV-1 RNA was detected at a level lower than the LLQ in eight, four, and nine additional samples by the LCx HIV RNA Quantitative, RealTime HIV, and COBAS AmpliPrep-COBAS TaqMan HIV-1 assays, respectively. Thus, the number of samples positive for HIV-1 RNA were 75 (82.4%) with the LCx HIV RNA Quantitative assay, 74 (81.3%) with the RealTime HIV assay, and 79 (86.8%) with the COBAS AmpliPrep-COBAS TaqMan HIV-1 assay (P = 0.57).
As shown in Table 1, a significant difference in the number of samples with HIV-1 RNA levels higher than the LLQ was not observed between the assays. CRF02_AG HIV-1 RNA could be detected at a level lower than the LLQ in two, one, and three additional samples by the LCx HIV RNA Quantitative, RealTime HIV, and COBAS AmpliPrep-COBAS TaqMan HIV-1 assays, respectively. Thus, the number of samples positive for CRF02_AG HIV-1 RNA were 8 (72.7%) with the LCx HIV RNA Quantitative assay, 10 (90.9%) with the RealTime HIV assay, and 10 (90.9%) with the COBAS AmpliPrep-COBAS TaqMan HIV-1 assay (P = 0.58).
As shown in Table 2, the HIV-1 RNA levels measured by the RealTime HIV assay in samples from subtype B-infected patients were lower than those obtained by either the LCx HIV RNA quantitative assay or the COBAS AmpliPrep-COBAS TaqMan HIV-1 test. Conversely, the HIV-1 RNA levels measured with the RealTime HIV assay in samples from patients infected with CRF02_AG HIV-1 strains were higher than those obtained with the two other assays, but these differences were not statistically significant.
As shown in Fig. 1, a high level of correlation between assays was observed, with Pearson's correlation coefficient (r) values ranging from 0.94 to 0.98. The agreement between methods was analyzed by using Bland-Altman plot analysis (3), and high levels of agreement were observed: 93.4% between the LCx HIV RNA Quantitative and the RealTime HIV assays as well as between the LCx HIV RNA Quantitative and the COBAS AmpliPrep-COBAS TaqMan HIV-1 assays and 94.5% between the RealTime HIV and the COBAS AmpliPrep-COBAS TaqMan HIV-1 assays (Fig. 2).
Taken together these data indicate that the three assays have similar performances for the quantitation of HIV-1 RNA in the samples tested in this study. The Abbott RealTime HIV assay and the COBAS AmpliPrep-COBAS TaqMan HIV-1 assay, both of which are supported by a fully automated extraction and both of which are based on real-time PCR, allow high throughputs (48 to 96 samples) and short turnaround times (nearly 3 h). This could be a major advantage for clinical laboratories.
In several studies, it has been reported that the LCx HIV RNA Quantitative assay is effective for quantitation of HIV-1 RNA in plasma samples from subjects infected with various group M subtypes, including CRF02_AG (15), or with group O viruses (14, 17). However, in one study, it has been reported that the performance of this assay is suboptimal only for the detection and quantification of CRF02_AG HIV-1 RNA (1). In the present study, HIV-1 RNA could be quantitated in 6 of 11 (54.5%) CRF02_AG-infected samples by the LCx HIV RNA Quantitative assay, whereas HIV-1 RNA could be quantitated in 7 (63.6%) and 9 (81.8%) of these samples by the COBAS AmpliPrep-COBAS TaqMan HIV-1 assay and the RealTime HIV assay, respectively. It was also observed that the HIV-1 RNA levels measured by the RealTime HIV assay were higher than those measured by the two other assays in the CRF02_AG-infected samples but were lower than those measured by the other two assays in subtype B-infected samples. These differences, however, did not reach statistical significance. This lack of significance could be due to small sample sizes. Therefore, larger studies are needed to better assess the possible impact of HIV-1 genetic diversity on the HIV-1 RNA levels measured by these assays.
ACKNOWLEDGMENTS
We acknowledge Abbott Molecular and Roche Diagnostics for providing test kits.
FOOTNOTES
Corresponding author. Mailing address: Laboratoire de Virologie, Hpital Saint-Eloi, 80 Avenue Augustin Fliche, 34295 Montpellier Cedex 05, France. Phone: (33) 467 337 127. Fax: (33) 467 337 793. E-mail: m-segondy@chu-montpellier.fr.
REFERENCES
Amendola, A., L. Bordi, C. Angeletti, E. Girardi, G. Ippolito, and M. R. Capobianchi. 2004. Comparison of LCx with other current viral load assays for detecting and quantifying human immunodeficiency virus type 1 RNA in patients infected with the circulating recombinant form A/G (CRF02). J. Clin. Microbiol. 42:811-815.
Berger, A., L. Scherzed, M. Sturmer, W. Preiser, H. W. Doerr, and H. F. Rabenau. 2002. Evaluation of the Cobas AmpliPrep/Cobas Amplicor HIV-1 Monitor Ultrasensitive test: comparison with the Cobas Amplicor HIV-1 Monitor test (manual specimen preparation). J. Clin. Virol. 25(Suppl. 3):S103-S107.
Bland, J. M., and D. G. Altman. 1999. Measuring agreement in method comparison studies. Stat. Methods Med. Res. 8:135-160.
de Mendoza, C., M. Koppelman, B. Montes, V. Ferre, V. Soriano, H. Cuypers, M. Segondy, and T. Oosterlaken. 2005. Multicenter evaluation of the Nuclisens EasyQ HIV-1 v1.1 assay for the quantitative detection of HIV-1 RNA in plasma. J. Virol. Methods 127:54-59.
Elbeik, T., W. G. Alvord, R. Trichavaroj, M. de Souza, R. Dewar, A. Brown, D. Chernoff, N. L. Michael, P. Nassos, K. Hadley, and V. L. Ng. 2002. Comparative analysis of HIV-1 viral load assays on subtype quantification: Bayer Versant HIV-1 RNA 3.0 versus Roche Amplicor HIV-1 Monitor version 1.5. J. Acquir. Immune Defic. Syndr. 29:330-339.
Erali, M., and D. R. Hillyard. 1999. Evaluation of the ultrasensitive Roche Amplicor HIV-1 MONITOR assay for quantitation of human immunodeficiency virus type 1 RNA. J. Clin. Microbiol. 37:792-795.
Erice, A., D. Brambilla, J. Bremer, J. B. Jackson, R. Kokka, B. Yen-Lieberman, and R. W. Coombs. 2000. Performance characteristics of the QUANTIPLEX HIV-1 RNA 3.0 assay for detection and quantitation of human immunodeficiency virus type 1 RNA in plasma. J. Clin. Microbiol. 38:2837-2845.
Holguin, A., B. Aracil, A. Alvarez, C. Barros, and V. Soriano. 2001. Prevalence of human immunodeficiency virus type 1 (HIV-1) non-B subtypes in foreigners living in Madrid, Spain, and comparison of the performances of the AMPLICOR HIV-1 MONITOR version 1.0 and the new automated version 1.5. J. Clin. Microbiol. 39:1850-1854.
Johanson, J., K. Abravaya, W. Caminiti, D. Erickson, R. Flanders, G. Leckie, E. Marshall, C. Mullen, Y. Ohhashi, R. Perry, J. Ricci, J. Salituro, A. Smith, N. Tang, M. Vi, and J. Robinson. 2001. A new ultrasensitive assay for quantitation of HIV-1 RNA in plasma. J. Virol. Methods 95:81-92.
Katsoulidou, A., M. Petrodaskalaki, V. Sypsa, E. Papachristou, C. G. Anastassopoulou, P. Gargalianos, A. Karafoulidou, M. Lazanas, T. Kordossis, A. Andoniadou, and A. Hatzakis. 2006. Evaluation of the clinical sensitivity for the quantification of human immunodeficiency virus type 1 RNA in plasma: comparison of the new COBAS TaqMan HIV-1 with three current HIV-RNA assays—LCx HIV RNA quantitative, Versant HIV-1 RNA 3.0 (bDNA) and COBAS AMPLICOR HIV-1 Monitor v1.5. J. Virol. Methods 131:168-174.
Muller, Z., E. Stelzl, M. Bozic, J. Haas, E. Marth, and H. H. Kessler. 2004. Evaluation of automated sample preparation and quantitative PCR LCx assay for determination of human immunodeficiency virus type 1 RNA. J. Clin. Microbiol. 42:1439-1443.
Parekh, B., S. Phillips, T. C. Granade, J. Baggs, D. J. Hu, and R. Respess. 1999. Impact of HIV type 1 subtype variation on viral RNA quantitation. AIDS Res. Hum. Retrovir. 15:133-142.
Segondy, M., T. D. Ly, M. Lapeyre, and B. Montes. 1998. Evaluation of the Nuclisens HIV-1 QT assay for quantitation of human immunodeficiency virus type 1 RNA in plasma. J. Clin. Microbiol. 36:3372-3374.
Swanson, P., B. J. Harris, V. Holzmayer, S. G. Devare, G. Schochetman, and J. Hackett. 2000. Quantification of HIV-1 group M (subtypes A-G) and group O by the LCx HIV RNA quantitative assay. J. Virol. Methods 89:97-108.
Swanson, P., C. de Mendoza, Y. Joshi, A. Golden, R. L. Hodinka, V. Soriano, S. G. Deware, and J. Hackett. 2005. Impact of human immunodeficiency virus type 1 (HIV-1) genetic diversity on performance of four commercial viral load assays: LCx HIV RNA Quantitative, AMPLICOR HIV-1 MONITOR v1.5, VERSANT HIV RNA 3.0, and NucliSens HIV-1 QT. J. Clin. Microbiol. 43:3860-3868.
Triques, K., J. Coste, J. L. Perret, C. Segarra, E. Mpoudi, J. Reynes, E. Delaporte, A. Butcher, K. Dreyer, S. Herman, J. Spadoro, and M. Peeters. 1999. Efficiencies of four versions of the AMPLICOR HIV-1 MONITOR test for quantification of different subtypes of human immunodeficiency virus type 1. J. Clin. Microbiol. 37:110-116.
Troonen, H., H. Grey, and G. Michel. 2002. Multicenter study of the LCx HIV RNA quantitative assay—a new competitive reverse transcriptase-PCR which targets pol genomic region of HIV-1 for the measurement of type B, non-type B and group O HIV-1 RNA. Clin. Chem. Lab. Med. 40:698-704.(Vincent Foulongne, Brigitte Montes, Mari)