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Journal of Clinical Microbiology, October 2009, p. 3266-3270, Vol. 47, No. 10
0095-1137/09/$08.00+0     doi:10.1128/JCM.00715-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Comparative Evaluation of the ExaVir Load Version 3 Reverse Transcriptase Assay for Measurement of Human Immunodeficiency Virus Type 1 Plasma Load {triangledown}

Wendy Labbett,1 Ana Garcia-Diaz,1 Zoe Fox,2 Gillian S. Clewley,1 Thomas Fernandez,3 Margaret Johnson,3 and Anna Maria Geretti1,3*

Department of Virology,1 Department of Infection and Population Health,2 Department of HIV Medicine, Royal Free Hampstead NHS Trust and University College London Medical School, London, United Kingdom3

Received 7 April 2009/ Returned for modification 22 May 2009/ Accepted 19 July 2009

In resource-limited settings, the virological monitoring of antiretroviral therapy is limited by high cost and the lack of infrastructure. The Cavidi ExaVir Load assay employs a simple and inexpensive enzyme-linked immunosorbent assay format to measure human immunodeficiency virus (HIV) reverse transcriptase activity, which correlates with plasma RNA load. The version 3 assay has been described as having improved precision and sensitivity. There are limited data on its performance relative to those of current real-time assays. Our objective was to compare HIV type 1 (HIV-1) RNA load measurement in plasma by ExaVir Load version 3 (designated ExaVir), Abbott M2000sp/M2000rt RealTime HIV-1 assay (designated RealTime), and Roche COBAS Ampliprep/COBAS TaqMan HIV-1 version 1 assay (designated TaqMan). Plasma from 119 patients (34 with subtype B infection, 85 with non-subtype B infection [A-H, CRF01, CRF02, CRF06, CRF12, CRF14, and complex]; 48 subjects were treatment experienced, 71 were naive) and serial dilutions of the second international standard (IS) were tested. Assay relationship and agreement were determined by linear regression, correlation analysis, and the Bland-Altman method. The ExaVir assay quantified 77/83 (92.8%) samples with viral loads of >2.3 log10 copies/ml by the molecular assays. Results were linearly associated and strongly correlated with RealTime and TaqMan measurements (R of 0.94 and 0.92, respectively) for both subtype B (R of 0.97 and 0.95, respectively) and non-subtype B (R of 0.93 and 0.91, respectively) samples. Mean differences were 0.28 and 0.18 log10 copies/ml in favor of the two molecular assays; 7/119 (5.9%) and 5/119 (4.2%) samples were outside the 95% level of agreement. ExaVir underquantified the IS by a mean of 0.2 (range, 0.0 to 0.5) log10 copies/ml. The ExaVir assay showed excellent concordance with real-time molecular assays, offering a suitable option for virological monitoring in settings with limited infrastructure.

* Corresponding author. Mailing address: Department of Virology, Royal Free Hampstead NHS Trust & UCL Medical School, Pond St., London NW3 2QG, United Kingdom. Phone: 44 20 7317 7521. Fax: 44 20 7830 2854. E-mail: a.geretti{at}medsch.ucl.ac.uk

{triangledown} Published ahead of print on 5 August 2009.

Journal of Clinical Microbiology, October 2009, p. 3266-3270, Vol. 47, No. 10
0095-1137/09/$08.00+0     doi:10.1128/JCM.00715-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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