gms | German Medical Science

Introduction: Cytomegalovirus (CMV) viral load is important for transplant recipients follow up and also important antiviral therapy monitorization. Around the world, many transplant centers monitorize their patients for CMV infections after transplantation by a commercial or a laboratory developed quantitative CMV PCR test. However since there is not any standardization for CMV PCR tests it is difficult to compare the results which collected in different laboratories and therefore each laboratory has to calculate their own cut off value for antiviral therapy. It could be a solution for standardization problem to calibrate or design the PCR test with the international CMV standard which introduced by WHO in 2012. However when quantitation is important it would be still difficult to compare the results when implementing a new test even it has WHO international standard (IS) for CMV. The aim of the study was to compare the results of two commercial quantitative CMV PCR tests, one of them with WHO IS for CMV.

Materials and methods: CMV DNA was investigated in 287 plasma samples of transplant recipients and 18 specimens prepared from QCMD 2011 panel by Cobas Amplicor CMV Monitor Test (CAMC) (Roche Diagnostics) and Cobas Taqman CMV Test (CTMC) (Roche Diagnostics) simultaneously. The former test was used for many years for CMV DNA detection and quantitaton in our laboratory and it was planned to be replaced with the latter test. After DNA extractions by Cobas Ampliprep (CAP) (Roche Diagnostics), both CAMC and CTMC were performed according to manufacturer's instructions for use. The detection of lower limits and quantification ranges for CACM and CTMC tests were; 600 copy/mL, 150 copy/mL and 600-100000 copy/mL, 150-100000000 copy/mL, respectively. At the beginning of the study information was given to the clinicians using the test results and during this process two tests results were reported together. The viral load results from the CAP/CACM and CAP/CTMC tests were compared in copies/mL using the receiver-operating characteristic (ROC) plot analysis and Spearman nonparametric correlation test using SPSS version 18.0.

Results: There is a good correlation between the results (r=0.878, p<0.001). Fourty samples were found negative and 156 samples were positive by both tests. One hundred and eighteen CMV DNA negative samples in the CAP/CACM test were CMV DNA positive by the CAP/CTM CMV test. There is only one sample which was CMV DNA positive by CAP/CACM but negative by CAP/CTMC. Discrepant results were mainly observed in samples containing low amounts of CMV DNA. Median viral loads for CAP/CAMC and CAP/CTMC tests were; 508 (range:0-3720000) copy /mL and 153 (range:0-10000000) copy/mL, respectively. It has been found that viral load levels of 600 copy/mL, 1000 copy/mL and 3000 copy/mL with CAP/CAMC test were corresponding to 432 copy/mL (393 IU/mL) (sensitivity 74.5%, specificity 97.5%), 557 copy/mL (507 IU/mL) (sensitivity 78.4%, specificity 97.2%) and 1590 copy/mL (1447 IU/mL) (sensitivity 81.3%, specificity 98.3%) with CAP/CTMC test, respectively.

Conclusion: In a clinical microbiology laboratory implementation of a new commercial CMV DNA PCR assay as CAP/CTMC test should be closely coordinated with clinicians and during this period the previous and the current tests need to be studied simultaneously.