Emergence of E138 mutations among treatment naïve HIV-infected patients in Istanbul

Abstract

No: 1689 Presentation at ESCV 2015: Poster 2 Interlaboratory comparison of BK virus DNA load assays M. Solis1,2,∗, M. Meddeb1, C. Sueur1,2, P. Domingo-Calap2, E. Soulier2, A. Chabaud1, P. Perrin3, B. Moulin4, S. Bahram4, S. Caillard3, F. Stoll-Keller1, S. Fafi-Kremer1 1 Laboratoire de Virologie, Hopitaux Universitaires de Strasbourg, Strasbourg, France 2 Inserm UMR S1109, LabEx Transplantex, Federation de Medecine Translationnelle de Strasbourg (FMTS), France 3 Departement de Nephrologie – Transplantation, Hopitaux Universitaires de Strasbourg, France 4 LabEx Transplantex, Federation de Medecine Translationnelle de Strasbourg (FMTS), Universite de Strasbourg, France Background: International guidelines recommend screening of kidney transplant recipients for BK virus (BKV) replication and define BKV viremia ≥4 log10 copies/ml as presumptive BKV-associated nephropathy (BKVN) and a cutoff for therapeutic intervention. Hence, BKV DNA load (BKVL) assays need to be comparable to ensure appropriate patient care. Methods: To assess interlaboratory variability in BKV viruria and viremia testing, 27 laboratories were sent 15 (5 urine, 5 whole blood and 5 plasma) and 8 (4 urine, 2 whole blood and 2 plasma) clinical specimens in 2013 and 2014, respectively. Results: Nine BKVL assays were used, including 5 commercial kits and 4 in-house methods. The majority (71%) of laboratories targeted the StAg while the LTAg was targeted by 17% of the laboratories and 3 other techniques used a different target gene (VP1, VP2-VP3 or VP1+StAg). Assuming that±0.5 log10 variation relative to the expected result is acceptable, 68% of the reported results fell within this range. Laboratories using commercial assays reported significantly more results within the acceptable range (76%) than laboratories using in-house assays (39%) (p<0.0001). High interlaboratory variability was observed, with a variation ranging from 1.73 to 4.65 log10 copies/ml (mean=2.55 log10 copies/ml). The number of mutations and the distance from the 3′ end of the primers largely contributed to this variability, and most mutations (88.2%)were genotype-specific. Genotype II and IV samples displayedhigher variability due to polymorphismon the target gene and were incorrectly quantified by all in-house assays. The calibration material also contributed to interlaboratory variability. Recalibration with a common calibrator significantly reduced the bias in comparisons between assays. Furthermore, the extraction apparatus had only a limited impact on interlaboratory variability. Conclusion: Polymorphism of the amplification target gene and the use of different calibration material contribute largely to interlaboratory variability. This variabilitymay significantly impact patient care and calls for presumptive BKVN cutoff reevaluation. The development of an International Standard for BKVL assay calibration and increased awareness of BKV polymorphism would reduce interlaboratoryvariabilityandallowadequateBKV infection monitoring. http://dx.doi.org/10.1016/j.jcv.2015.07.264