Introduction: Nucleic acid test window periods for HIV, HCV, and HBV facilitate the estimation of the residual risk of unexpected disease transmission. In 2010, consensus window periods were published based on contemporaneous assays.

Objectives: The objective of this analysis was to provide revised estimates of the NAT window periods based on the assay currently used by the Australian Red Cross Blood Lifeblood.

Method: Window periods were calculated by a published method estimating the time a from single infective particle appearance in the inoculum (20ml) until plasma concentrations reach the assay's limit of detection (X50 or X95 for 50% and 95% limit of detection). The method assumes linear viral doubling times of 0.85, 0.45, and 2.56 days and conversion factors for IU per ml to copies per ml of 0.6, 3.4, and 5 for HIV, HCV, and HBV respectively. Manufacturer-specified detection limits for the Procleix® Ultrio Elite® Assay (Grifols Diagnostic Solutions Inc. California, USA) were utilised.

Results: Calculated X50 window periods were 5.1 (4.6 - 5.9), 2.7 (2.4 – 3.0), and 16.6 (14.5 - 19.3) days for HIV, HCV, and HBV respectively. Calculated X95 window periods were 6.6 (5.9 - 7.6), 3.5 (3.2 - 3.8), and 22.4 (19.6 – 26.0) days, respectively.

Conclusion: Use of the Procleix® Ultrio Elite® Assay is associated with X50 NAT window periods that are significantly shorter for HBV and sit at the lower range of previously published estimates for HIV and HCV.  The X95 estimates highlight the period after which a negative assay is clinically reliable.