Related Experiment Video
Updated: Jan 14, 2026
Dried Blood Spots - Preparing and Processing for Use in Immunoassays and in Molecular Techniques
Published on: March 13, 2015
HBV deferrals and NAT window period: Assessing the impact of 3-month versus 4-month testing delays
Antoine Lewin1, Marc Germain1, Sylvie Lachance1
1Medical Affairs and Innovation, Héma-Québec, Montreal, Quebec, Canada.
Insights
A 3-month deferral for blood donors after hepatitis B virus (HBV) exposure poses a negligible risk compared to 4 months. This change can increase the donor pool without compromising blood safety.
Area of Science:
- Blood Transfusion Safety
- Virology
- Public Health Policy
Background:
- Current Héma-Québec policy defers donors for 3, 6, or 12 months based on hepatitis B virus (HBV) risk factors.
- This complex policy may unnecessarily defer safe donors and cause confusion.
- Published window period estimates suggest a uniform 3- or 4-month deferral may be sufficient.
Purpose of the Study:
- To estimate the incremental risk of adopting a 4-month HBV deferral period versus a 3-month period.
- To inform Héma-Québec's policy update regarding donor deferral periods for HBV.
Main Methods:
- A probit analysis adapted from the Weusten model was used.
- The study considered the Procleix Ultrio plus nucleic acid test (NAT)-HBV assay and HBV viral dynamics.
- Monte Carlo simulations of 10,000 infected donors were performed to evaluate incremental risk.
Main Results:
- The NAT window period was estimated at 34.5 days (LOD50) and 28.2 days (LOD95).
- Simulations indicated that 32 donors (or 104 with an 8-day eclipse phase) would test NAT-negative between 3-4 months post-exposure.
- This corresponds to an estimated one HBV contamination every 7.8 million (or 2.4 million) donations.
Conclusions:
- A 3-month HBV deferral period presents a negligible incremental risk compared to a 4-month period.
- Adopting a 3-month deferral is acceptable and will increase the number of eligible blood donors.
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.
