A three-center European external quality control study of PCR for detection of cytomegalovirus DNA in blood

The presence of cytomegalovirus (CMV) in the blood has important consequences for patient management, and an external quality control study of its detection by the PCR was conducted by the Infectious Disease Working Party of the European Group for Blood and Marrow Transplantation. Forty-eight coded peripheral blood samples from bone marrow transplant recipients were processed in parallel in three European centers by using the routine in-house PCR assay. Protocols varied in choice of primers, specificity and amplificability controls, and sample processing. Results for 38 of 47 samples agreed, 35 being negative and 3 positive. Of the 12 samples reported as positive by at least one center, only 3 were found to be positive by all three centers, 1 was found to be positive by two centers, and the remaining 8 were found to be positive by one center only. The nine discrepant samples appeared to contain around 1,000-fold less viral DNA than the three concordant positive samples, CMV detection was affected both by the number of leukocytes from which DNA was extracted and by the number of cell equivalents added per PCR. External quality control schemes for CMV PCR are clearly necessary in order to compare data from different centers, and recommendations for standardizing the PCR detection of CMV in blood leukocytes are made.