HBV deferrals and NAT window period: Assessing the impact of 3-month versus 4-month testing delays.

BACKGROUND

Héma-Québec (Québec, Canada) currently defers prospective blood donors for 3, 6, or 12 months depending on their self-reported risk factors for hepatitis B virus (HBV) infection. However, this policy may be needlessly complex and overly cautious, thereby potentially causing confusion among donors and deferring those with an acceptable safety profile. Based on published window period estimates, a uniform deferral period of 3 or 4 months may be considered. To inform our policy update, we estimated the incremental risk of adopting an HBV deferral period of 4 months versus 3 months.

STUDY DESIGN AND

METHODS

This probit analysis was an adaptation of the Weusten model. The analysis considered the characteristics of the current nucleic acid test (NAT)-HBV assay (i.e., Procleix Ultrio plus assay in minipools of 16) and HBV viral dynamics. The incremental risk of banking an HBV-contaminated whole blood donation was evaluated through a Monte-Carlo simulation in which 10,000 infected donors were simulated; corresponding to 833 years of observation.

RESULTS

The window period for the NAT 50% endpoint limit of detection (LOD50) was estimated at 34.5 days (range = 12.4-136.5), and 28.2 days (range = 10.1-111.4) for the LOD95. Of the 10,000 simulated infected donors, 32 (and 104 using an eclipse phase [EP] of 8 days) would test negative by NAT between 3 and 4 months post-HBV exposure, corresponding to one HBV contamination every 7.8 (or 2.4 using the 8-day EP) million donations.

DISCUSSION: Adopting an HBV deferral of 3 months poses a negligible incremental risk compared with 4 months and is acceptable given the resulting gain in newly eligible donors.