Comparative Evaluation of In-House PCR and Commercial TTV R-GENE Assays for Torque Teno Virus Quantification: an Agreement and Reliability Study

BACKGROUND:The non-pathogenic Torque Teno Virus (TTV) is currently being investigated as a functional biomarker for the degree of immunosuppression. A reliable assay for quantification of TTV is extremely important. The primary objective of this study was to assess the reliability and agreement between two quantitative methods, an in-house PCR assay and the commercial TTV R-GENE, for the detection of TTV viral loads. The secondary objectives included testing of the in-house assay by performing external quality assessment (EQA) and assessing the TTV prevalence in 101 Danish blood donors. METHODS:Parallel TTV viral load quantification by both PCR assays was conducted in samples from heart transplant recipients, kidney transplant recipients, and patients with atopic dermatitis. Bland-Altman statistics and Intraclass Correlation Coefficient (ICC) were implemented for the evaluation of agreement and reliability between assays. Additionally, 12 EQA samples and samples from 101 blood donors were analyzed applying the in-house assay. RESULTS:Qualitative comparison revealed a high concordance (80.6%) between assays. Bland-Altman statistics demonstrated a mean difference of 0.72 Log10 copies/mL. with the highest viral loads obtained with the in-house assay. Reliability, defined with an ICC of 0.82, was considered good. All EQA samples were acceptable. The prevalence of TTV in Danish blood donors was 60.4%. CONCLUSION:This study demonstrated qualitative concordance, and moderate agreement and reliability between an in-house assay and the commercial TTV R-GENE kit. The in-house assay obtained acceptable results within the EQA, suggesting that the in-house assay is suitable for quantification of TTV viral loads in clinical practice.