Commutability of the First World Health Organization International Standard for Human Cytomegalovirus

Abstract

Quantitative detection of cytomegalovirus (CMV) DNA has become a standard part of care for many groups of immunocompromised patients; recent development of the first WHO international standard for human CMV DNA has raised hopes of reducing interlaboratory variability of results. Commutability of reference material has been shown to be necessary if such material is to reduce variability among laboratories. Here we evaluated the commutability of the WHO standard using 10 different real-time quantitative CMV PCR assays run by eight different laboratories. Test panels, including aliquots of 50 patient samples (40 positive samples and 10 negative samples) and lyophilized CMV standard, were run, with each testing center using its own quantitative calibrators, reagents, and nucleic acid extraction methods. Commutability was assessed both on a pairwise basis and over the entire group of assays, using linear regression and correspondence analyses. Commutability of the WHO material differed among the tests that were evaluated, and these differences appeared to vary depending on the method of statistical analysis used and the cohort of assays included in the analysis. Depending on the methodology used, the WHO material showed poor or absent commutability with up to 50% of assays. Determination of commutability may require a multifaceted approach; the lack of commutability seen when using the WHO standard with several of the assays here suggests that further work is needed to bring us toward true consensus. Q uantitative detection of cytomegalovirus (CMV) DNA has become a standard part of care for many groups of immunocompromised patients, but particularly for transplant recipients (1-4). A host of laboratory-developed real-time PCR methods have been described for this purpose, and more recently, FDAapproved assays have become available. The benefits of such testing to trigger preemptive or therapeutic treatments or to monitor the efficacy of such treatments and determine therapeutic endpoints are widely accepted. However, benchmark values for such interventions have yet to be established, and it is now decades after the introduction of molecular diagnostics. The reasons for this lack of consensus have become clear over a number of studies which have shown poor quantitative concordance between laboratories and between methods. Several investigators have documented discordant results for human cytomegalovirus (HCMV) testing as well as for other viral load measures that depend largely upon methods developed in the laboratory (5-7). The reasons for such variability may be numerous (8); however, intuitively, different quantitative calibrators may directly relate to different quantitative results. This has been confirmed in the literature, and the importance of developing consensus standards has been well accepted (9-11) and confirmed by past experience with other viruses.The advent of the first WHO International Standard for HCMV DNA was meant to address this need (12). This material consists of a known quantity of the CMV merl...

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