A new highly automated extraction system for quantitative real-time PCRs from whole blood samples: Routine monitoring of opportunistic infections in immunosuppressed patients

Performance Evaluation of the Real-Q Cytomegalovirus (CMV) Quantification Kit Using Two Real-Time PCR Systems for Quantifying CMV DNA in Whole Blood

Standardized cytomegalovirus (CMV) DNA quantification is important for managing CMV disease. We evaluated the performance of the Real-Q CMV Quantification Kit (Real-Q assay; BioSewoom, Korea) using whole blood (WB), with nucleic acid extraction using MagNA Pure 96 (Roche Diagnostics, Germany). Real-time PCR was performed on two platforms: the 7500 Fast real-time PCR (7500 Fast; Applied Biosystems, USA) and CFX96 real-time PCR detection (CFX96; Bio-Rad, USA) systems. The WHO international standard, diluted with CMV-negative WB, was used to validate the analytical performance. We used 90 WB clinical samples for comparison with the artus CMV RG PCR kit (artus assay; Qiagen, Germany). Limits of detections (LODs) in 7500 Fast and CFX96 were 367 and 479 IU/mL, respectively. The assay was linear from the LOD to 10⁶ IU/mL (R² ≥0.9886). The conversion factors from copies to IU in 7500 Fast and CFX96 were 0.95 and 1.06, respectively. Compared with the artus assay, for values <1,000 copies/mL, 100% of the samples had a variation <0.7 log₁₀ copies/mL; >1,000 copies/mL, 73.3% and 80.6% of samples in 7500 Fast and CFX96, respectively, had <0.5 log₁₀ copies/mL. The Real-Q assay is useful for quantifying CMV in WB with the two real-time PCR platforms.

Quantification of cytomegalovirus viral load

Cytomegalovirus (CMV), a member of the Herpesviridae family, is worldwide distributed. After the primary infection, CMV induces a latent infection with possible reactivation(s). It is responsible for severe to life-threatening diseases in immunocompromised patients and in foetuses and newborns of infected mothers. For monitoring CMV load, classical techniques based on rapid culture or pp65 antigenemia are progressively replaced by quantitative nuclear acid tests (QNAT), easier to implement and standardize. A large variety of QNAT are available from laboratory-developed assays to fully-automated commercial tests. The indications of CMV quantification include CMV infection during pregnancy and in newborns, and viral surveillance of grafted and non-grafted immunocompromised patients, patients with bowel inflammatory diseases and those hospitalised in intensive care unit. A close cooperation between virologists and clinicians is essential for optimizing the benefit of CMV DNA monitoring.

Fully automated quantification of cytomegalovirus (CMV) in whole blood with the new sensitive Abbott RealTime CMV assay in the era of the CMV international standard

Fully standardized reproducible and sensitive quantification assays for cytomegalovirus (CMV) are needed to better define thresholds for antiviral therapy initiation and interruption. We evaluated the newly released Abbott RealTime CMV assay for CMV quantification in whole blood (WB) that includes automated extraction and amplification (m2000 RealTime system). Sensitivity, accuracy, linearity, and intra- and interassay variability were validated in a WB matrix using Quality Control for Molecular Diagnostics (QCMD) panels and the WHO international standard (IS). The intra- and interassay coefficients of variation were 1.37% and 2.09% at 5 log10 copies/ml and 2.41% and 3.80% at 3 log10 copies/ml, respectively. According to expected values for the QCMD and Abbott RealTime CMV methods, the lower limits of quantification were 104 and <50 copies/ml, respectively. The conversion factor between international units and copies (2.18), determined from serial dilutions of the WHO IS in WB, was significantly different from the factor provided by the manufacturer (1.56) (P = 0.001). Results from 302 clinical samples were compared with those from the Qiagen artus CMV assay on the same m2000 RealTime system. The two assays provided highly concordant results (concordance correlation coefficient, 0.92), but the Abbott RealTime CMV assay detected and quantified, respectively, 20.6% and 47.8% more samples than the Qiagen/artus CMV assay. The sensitivity and reproducibility of the results, along with the automation, fulfilled the quality requirements for implementation of the Abbott RealTime CMV assay in clinical settings. Our results highlight the need for careful validation of conversion factors provided by the manufacturers for the WHO IS in WB to allow future comparison of results obtained with different assays.