title: Calibration of BK Virus Nucleic Acid Amplification Testing to the 1st WHO International Standard for BK Virus.
abstract: Significant interassay variability in the quantification of BK virus (BKV) DNA precludes establishing broadly applicable thresholds for the management of BKV infection in transplantation. The 1st WHO International Standard for BKV (primary standard) was introduced in 2016 as a common calibrator for improving the harmonization of BKV nucleic acid amplification testing (NAAT) and enabling comparisons of biological measurements worldwide. Here, we evaluated the Altona RealStar BKV assay (Altona) and calibrated the results to the international unit (IU) using the Exact Diagnostics BKV verification panel, a secondary standard traceable to the primary standard. The primary and secondary standards on Altona had nearly identical linear regression equations (primary standard, Y = 1.05X - 0.28,R2= 0.99; secondary standard, Y = 1.04X - 0.26,R2= 0.99) and conversion factors (primary standard, 1.11 IU/copy; secondary standard, 1.09 IU/copy). A comparison of Altona with a laboratory-developed BKV NAAT assay in IU/ml versus copies/ml using Passing-Bablok regression revealed similar regression lines, no proportional bias, and improvement in the systematic bias (95% confidence interval of intercepts: copies/ml, -0.52 to -1.01; IU/ml, 0.07 to -0.36). Additionally, Bland-Altman analyses revealed a clinically significant reduction of bias when results were reported in IU/ml (IU/ml, -0.10 log10; copies/ml, -0.70 log10). These results indicate that the use of a common calibrator improved the agreement between the two assays. As clinical laboratories worldwide use calibrators traceable to the primary standard to harmonize BKV NAAT results, we anticipate improved interassay comparisons with a potential for establishing broadly applicable quantitative BKV DNA load cutoffs for clinical practice.
authors.affiliation: Department of Medicine, Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Susanna K
authors.initials: SK
authors.lastname: Tan
authors.affiliation: Clinical Virology Laboratory, Stanford Health Care, Stanford, California, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Milligan
authors.affiliation: Department of Pathology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Malaya K
authors.initials: MK
authors.lastname: Sahoo
authors.affiliation: Clinical Virology Laboratory, Stanford Health Care, Stanford, California, USA.
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Taylor
authors.affiliation: Department of Medicine, Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, California, USA bpinsky@stanford.edu.|Clinical Virology Laboratory, Stanford Health Care, Stanford, California, USA.|Department of Pathology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Benjamin A
authors.identifier: 0000-0001-8751-4810
authors.initials: BA
authors.lastname: Pinsky
mesh_terms: D001739:BK Virus / Q000302:isolation & purification*; D002138:Calibration; D006801:Humans; D025202:Molecular Diagnostic Techniques / Q000379:methods* / Q000592:standards*; D021141:Nucleic Acid Amplification Techniques / Q000379:methods* / Q000592:standards*; D027601:Polyomavirus Infections / Q000175:diagnosis*; D015203:Reproducibility of Results; D014412:Tumor Virus Infections / Q000175:diagnosis*
keywords: molecular methods; polyomavirus