Positioning of run controls for ensuring sufficient analytical sensitivity of assays

Document VR4059 describes how the reactivity of the Ultrio and cobas MPX versions on the inactivated HBV, HCV and HIV-1 standard dilutions has been used to design ViraQ Check and Trend Controls at close distance to the 95% LOD of these NAT methods. The correct positioning of run controls is essential for ensuring sufficient analytical sensitivity of the NAT systems. Validation report VR4061 describes how the analytical sensitivity of individual NAT reagent batches and instruments can be monitored by specific ViraQ Controls. The positioning of the ViraQ Controls near the detection limits of the blood screening NAT assays has been shown to be instrumental in recognizing reagent batches with significantly lower analytical sensitivity than claimed by the manufacturer. This alert function of our run controls would not be possible if we had not established the viral concentration in relation to the detection limits of the assays, and if we would not be able to guarantee consistent viral concentrations in consecutive batches of the controls over time. Note that laboratories using too high viral concentrations in run controls will not be alerted for poor performance of the Ultrio assay versions because the run control will still give the same saturated response levels if the analytical sensitivity of the NAT system is significantly reduced. Also the HBsAg, anti-HIV and anti-HIV concentrations in SeraQ Multi-Marker Controls for viral serology are near the detection limits and help ensuring that the analytical sensitivity and length of the diagnostic window periods remain constant over time.