CLINICAL AND TRANSLATIONAL RESEARCH The Clinical Utility of Whole Blood Versus Plasma Cytomegalovirus Viral Load Assays for Monitoring Therapeutic Response Luiz F. Lisboa, 1 Anders Åsberg, 2 Deepali Kumar, 1 Xiaoli Pang, 3 Anders Hartmann, 4 Jutta K. Preiksaitis, 1 Mark D. Pescovitz, 5 Halvor Rollag, 6 Alan G. Jardine, 7 and Atul Humar 1,8 Background. In patients with cytomegalovirus (CMV) disease, regular monitoring of viral loads and treatment until negative are recommended. However, with more sensitive polymerase chain reaction (PCR) assays and cellular periph- eral sample types, detection of low-level viremia is achievable. We compared a whole blood real-time PCR with a plasma PCR assay for monitoring therapeutic response. Methods. Patients enrolled in a trial to treat CMV disease for 21 days had regular viral load monitoring. The results of a plasma-based PCR assay were compared with a real-time PCR assay of whole blood and assessed for their ability to predict recurrence. Results. In 219 evaluable patients, viral loads in plasma versus whole blood demonstrated good correlation but signif- icant difference in absolute value and clearance kinetics. Virus was still detectable by day 21 in 154 of 219 (70.3%) patients with the whole blood versus 105 of 219 (52.1%; P0.001) patients with the plasma assay. The positive predictive value of persistent plasma viremia at day 21 for virologic recurrence was 41.9% vs. 36.3% for the whole blood assay. In the subset of patients with a negative plasma but positive whole blood at day 21 (n=49), the incidence of virologic recurrence was similar to that of all patients with a negative plasma assay (23.1% vs. 23.6%). Conclusions. When treating CMV disease, enhanced detection of residual viremia using a whole blood real-time PCR does not seem to offer significant clinical advantages nor allows for better prediction of recurrence of CMV viremia or disease. The treat-to-negative paradigm may not hold true when such assays are used. Keywords: Organ transplantation, Viral infection, Real-time PCR, Outcome. (Transplantation 2011;91: 231–236) T herapy of cytomegalovirus (CMV) viremia or active CMV disease with ganciclovir is usually successful. How- ever, a commonly encountered clinical question revolves around the duration of antiviral therapy so as to avoid recur- rence after treatment is stopped. Based on the current guide- lines for the management of CMV viremia in solid-organ transplant recipients, the standard approach is to perform weekly molecular monitoring (with a quantitative CMV viral load assay using nucleic acid testing or pp65 antigenemia as- say) and continue antiviral therapy until viremia is no longer detectable (1, 2). With pp65 antigenemia or with nucleic acid testing of plasma samples, this usually results in treatment duration of between 2 and 4 weeks. The rational for this “treat until negative” paradigm is based on high rates of recurrent viremia or recurrent clinical disease observed when the anti- viral treatment is discontinued before undetectable CMV lev- els are achieved (3–5). Rapid advances in molecular techniques, specifically the use of real-time polymerase chain reaction (PCR)-based assays, have resulted in the development of progressively more sensitive assays, thereby lowering the achievable detec- Presented in part at the American Transplant Congress, May 30 to June 3, 2009, Boston, MA. 1 Transplant Infectious Diseases, Department of Medicine, University of Al- berta, Edmonton, AB, Canada. 2 Department of Pharmaceutical Biosciences, University of Oslo, School of Pharmacy, Oslo, Norway. 3 Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, AB, Canada. 4 Department of Medicine, University of Oslo, Oslo University Hospital, Rikshospitalet, Oslo, Norway. 5 Department of Surgery, Indiana University, Indianapolis, IN. 6 Department of Microbiology, University of Oslo and Oslo University Hos- pital, Oslo, Norway. 7 BHF Cardiovascular Research Centre, University of Glasgow, Glasgow, United Kingdom. 8 Address correspondence to: Atul Humar, M.D., Transplant Infectious Dis- eases, University of Alberta, Room 6-030 Katz Group—Rexall Centre for Health Research, Edmonton, AB, Canada T6G 2E1. E-mail: ahumar@ualberta.ca L.F.L. and A.H. participated in writing of the article and data analysis; A.Å., A.H., M.D.P., H.R., and A.G.J. participated in clinical trial design and execution; A.Å., D.K., X.P., A.H., J.K.P., M.D.P., H.R., and A.G.J. participated in review of the article; D.K. and A.H. participated in research design; X.P., J.K.P., and A.H. participated in development of analytic tool; and D.K., X.P., J.K.P., A.H. participated in performance of the laboratory analysis. Received 28 June 2010. Revision requested 7 July 2010. Accepted 30 September 2010. Copyright © 2011 by Lippincott Williams & Wilkins ISSN 0041-1337/11/9102-231 DOI: 10.1097/TP.0b013e3181ff8719 Transplantation • Volume 91, Number 2, January 27, 2011 www.transplantjournal.com | 231