Calibration of viral standards in nucleic acid copies or virion numbers

We have used the bDNA 3.0 assay as the reference method for quantification in viral nucleic acid copies or genome equivalents. The molecular standards used in this multi-probe assay were quantified by three physico-chemical techniques. The concentrations of our viral standards in copies/mL was determined by multiple replicate bDNA 3.0 tests over the years and compared with the quantitative results of other NAT methods (that often gave comparable results). The number of detectable nucleic acid molecules in a viral standard by a NAT method can be calculated from the Poisson distribution in limiting standard dilutions. From the large amount of replicate test results on standard dilutions in the blood screening NAT assays it was estimated that (as expected) around 80-90% detection efficiency can be achieved by the most sensitive methods. These data further support that the quantification of our viral standards in nucleic acid copies with the bDNA3.0 assay was likely close to true virion numbers. The calibration in copies or virion numbers has been fundamental for estimating the lengths of the infectious window periods and residual transfusion-transmission risk. (The infectious window period ramp up phase starts when the concentration reaches one virion per blood component). For that reason we decided to primarily express the viral concentration of our reference panels and controls for HBV, HCV and HIV in copies/mL.

Read more about the calibration of the native VQC-Sanquin and inactivated BQC standards in nucleic acid copies in this validation report (PDF).