Multicenter Evaluation of Whole-Blood Epstein-Barr Viral Load Standardization Using the WHO International Standard

Abstract

The first WHO international standard for Epstein-Barr virus (EBV) (WHO EBV standard) for nucleic acid amplification technology (NAT)-based assays was commercialized in January 2012 by the National Institute for Biological Standards and Control. In the study reported here, we compared whole-blood EBV DNA load (EDL) results from 12 French laboratories for seven samples (Quality Controls for Molecular Diagnostics 2013 proficiency panel) in order to determine whether expression in international units reduces interlaboratory variability in whole-blood EDLs. Each testing laboratory used a conversion factor to convert EDL results from copies per milliliter to international units per milliliter. This conversion factor was calculated from the WHO EBV standard according to the protocol described in this study (nine laboratories) or the recommendations of the PCR kit suppliers (three laboratories). The interlaboratory variability in whole-blood EDL results was reduced after standardization of the results using the WHO EBV standard. For the seven samples tested, standard deviations (SD) ranged from 0.41 to 0.55 when the results were expressed in log copies per milliliter, whereas the SD ranged from 0.17 to 0.32 when results were given in log international units per milliliter. Comparing the variance data (F test), we showed that the dispersion of whole-blood EDL results was significantly lower when they were expressed in log international units per milliliter (P < 0.001 for six of seven samples and P < 0.05 for one sample with a low mean EDL of 2.62 log IU/ml). This study showed that the use of the WHO EBV standard could improve the homogeneity of whole-blood EDL results between laboratories as well as the monitoring of patients at high risk of posttransplant lymphoproliferative disorders or other EBV-associated diseases. Primary Epstein-Barr virus (EBV) infection is the cause of the vast majority of cases of infectious mononucleosis and the subsequent lifelong persistence of EBV in the host, which, although mostly asymptomatic, can lead to the development of several lymphoid and epithelial cancers in immunosuppressed and immunocompetent individuals (1, 2).With the rapid development of real-time quantitative PCR, the measurement of EBV DNA load (EDL) during these EBV-associated diseases has been largely implemented in clinical practice (3-5). The monitoring of EDL in blood is required for transplant recipients at risk of posttransplantation lymphoproliferative disorders (PTLDs) and could also be a surrogate marker for the adjustment of the immunosuppressive regimen in these patients (6, 7). EDL measurement in plasma also appears to be a useful biomarker for the management of EBV-associated undifferentiated nasopharyngeal carcinoma (8). Although less clearly demonstrated, EDL measurements could also be helpful in other clinical situations such as severe or atypical infectious mononucleosis and other EBV-associated malignancies in immunosuppressed or immunocompetent patients (3, 9).Besides the debates on the clinical utility ...

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