Kinetics of human cytomegalovirus (HCMV) DNAemia in transplanted patients expressed in international units as determined with the Abbott RealTime CMV assay and an in-house assay.

Background: Consensus human cytomegalovirus (HCMV) DNA cut-off values for preemptive therapy in transplant recipients have not yet been defined, mainly due to the lack of real-time PCR standardization. Objectives: (i) To compare the kinetics of HCMV DNA in transplanted patients using an in-house real-time PCR assay (Pavia assay) and the new Abbott RealTime CMV assay; (ii) to verify assay concordance in the identification of patients eligible for preemptive treatment and (iii) standardize results with international units (IUs) using the WHO International HCMV DNA Standard as a reference. Study design: The kinetics of HCMV disseminated infection was retrospectively evaluated in 513 stored whole blood samples from 37 transplanted patients enrolled in randomized prospective studies designed for the clinical validation of HCMV DNA cut-off values. Conversion factors of HCMV DNA copy number to WHO international units (IUs) were determined. Results: Among the 513 samples, 352 (68.6%) were concordant positive, 42 (8.1%) concordant negative and 119 (23.1%) discordant. All discordant samples resulted positive by the Abbott RealTime CMV assay and negative by the Pavia assay, showing higher sensitivity for the Abbott RealTime CMV assay. A significant correlation was observed between concordant positive samples (r = 0.89). HCMV DNAemia determined by each assay showed overlapping kinetics. Expression of results as IU/ml provided the best results in preemptive treatment simulation. Conclusion: HCMV DNAemia cut-off values determined using our in-house assay and expressed as IU/ml appear valid for use in commercial assays as well as other potential in-house assays.