Blood Donation, Components & Safety: Winning Abstract 2017
Can we apply the standard residual risk estimates model to calculate HEV risk among NHSBT’s apheresis donors?
K. Davison, C. Reynolds, A. Kitchen & S. Brailsford
Public Health England, London
NHS Bloodand Transplant, London
Mathematical models to estimate the residual risk of routine screening assays not detecting HBV, HCV or HIV in donations made in the window period (WP) are well established. Hepatitis E Nucleic Acid Testing (HEVNAT) was implemented by NHSBT in February 2016 for all apheresis donors and sufficient whole blood donors to meet the predicted need for HEV RNA negative products; here the traditional methodology is applied to HEV testing data to estimate residual risk in apheresis donors.
Using PULSE, the NHSBT donor/donation register, details of donations from apheresis donors tested were extracted. HEV RNA positivity rate was estimated among donations and donors, and compared by age-group and gender. Incidence was assumed to be equal to the positivity rate in donors; to estimate risk this was multiplied by 0.019 for the WP in years. Risk was also calculated by age-group and gender, and weighted by the number of donations in each strata to give an overall adjusted value. Ranges of risk were based on the upper and lower 95% confidence intervals of incidence estimates.
Between February and December 2016 73,392 donations from 18,869 apheresis donors were tested using HEV NAT on pools of 24 donation samples; 24 donations were positive. Donors are re-instated once shown to be HEV RNA negative with >=1 IU/ml IgG, usually within 2-months of the index donation. The average number of donations was 4.2 for males and 2.4 for females, with a maximum of 22 and 18 respectively.
HEV RNA positivity was highest for males aged 17-24 at 2.1/1000 donations, or 5.6/1000 donors. HEV residual risk was estimated as 2.44/100,000 donations (range 1.56/100,000-3.63/100,000); the weighted estimate was marginally greater at 2.49/100,000.
Using the standard approach and the very conservative estimate of a 7 days WP for NAT, HEV risk was estimated to be high. This has increased from 0.68/100,000 estimated previously among South East England donors using the same WP. Despite the different donation rates among male and female age groups, weighting of the risk had little overall impact.This method will be adapted for use in whole blood donor following the introduction of universal testing.
