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 ϭ 1.05X Ϫ 0.28, R 2 ϭ 0.99; secondary standard, Y ϭ 1.04X Ϫ 0.26, R 2 ϭ 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 PassingBablok regression revealed similar regression lines, no proportional bias, and improvement in the systematic bias (95% confidence interval of intercepts: copies/ml, Ϫ0.52 to Ϫ1.01; IU/ml, 0.07 to Ϫ0.36). Additionally, Bland-Altman analyses revealed a clinically significant reduction of bias when results were reported in IU/ml (IU/ml, Ϫ0.10 log 10 ; copies/ml, Ϫ0.70 log 10 ). 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.

Prediction of BK viremia by urine viral load in renal transplant patients: An analysis of BK viral load results in paired urine and plasma samples

“…Most institutions use in‐house techniques for quantitative BKPyV PCR methods, which result in marked variability among the assays and prevent inter‐laboratory comparison of results . Consequently, the first WHO International Standard for BKPyV infection was introduced in 2016 to reduce inter‐laboratory variability and permit comparison of BKPyV load worldwide . The comparable unit is called the international unit (IU) and has been introduced to other viral load testing including Cytomegalovirus (CMV) and Epstein‐Barr Virus (EBV) …”

“…10 Consequently, the first WHO International Standard for BKPyV infection was introduced in 2016 to reduce inter-laboratory variability and permit comparison of BKPyV load worldwide. 11 The comparable unit is called the international unit (IU) and has been introduced to other viral load testing including Cytomegalovirus (CMV) and Epstein-Barr Virus (EBV). [12][13][14] The present study was undertaken to compare, in IU/mL, the urine and the plasma BKPyV levels in a large data set (>1000) of paired urine and plasma specimens (collected in the same patient on the same day) in renal transplant recipients.…”

Standardization of Nucleic Acid Tests: the Approach of the World Health Organization

“…Using next-generation sequencing data, even subpopulations of sequence variants are being detected, as was reported recently for the ISs for BKV and JCV (64,65). Passage of the strains in cell culture resulted in heterogeneous DNA populations, the reason for which is not understood and which could affect some specialized assays (64,65), although both preparations were shown to harmonize assay performance successfully in the collaborative studies (11,12) and in independent studies (66). These observations demonstrate the importance of thorough characterization of the starting materials used for standard preparation.…”

New England BK consortium: Regional survey of BK screening and management protocols in comparison to published consensus guidelines

“…The desire for a universally calibrated PCR standard has been identified as a major area of need by the World Health Organization . As a way of understanding the differences seen from center‐to‐center and laboratory‐to‐laboratory, our group has decided to undertake a small study evaluating the impact of local specimens analyzed by the site's preferred method (ie, internal laboratory or send‐out) vs a control laboratory where all participating centers will send a discarded sample.…”