Tissue Donor Safety Study Group
The second study evaluated data from 11,400 tissue donors to estimate their window-period risk. The test samples came from five AATB banks: American Red Cross, Community Blood and Tissue Services, LifeNet, Musculoskeletal Transplant Foundation, and Northwest Tissue Services.
The study concluded that risks for tissue donors were higher than volunteer blood donors, but lower than the general public. Those risks will be reduced in direct relation to the narrowing of the window period, as they were for blood donors in the first study. For tissue donors, NAT should reduce the risk of undetected HIV and hepatitis B (HBV) three-fold and the risk of HCV ten-fold (see graphic).
Based on 20,000 tissue donors per year and the estimates from the study, NAT’s ability to improve safety by reducing window periods for infected donors would catch one donor with HIV every 4 years, one with HCV every 2.3 years, and one with HBV every 2.6 years. NAT might prevent even more infection transmissions if current inventories, as well as new donors, were tested.
Why Wait?
With the study results clearly showing the value of NAT, why was its use not mandated earlier?
As noted, some individual tissue banks instituted NAT months ago. AATB’s position was more complicated, however.
The performance—both in terms of sensitivity and specificity—of NAT test kits had not been evaluated for cadeveric blood, which is often the only type of sample available from potential tissue donors. Hemolysis, the naturally occurring breakdown of blood after death, could affect NAT results, and that factor could lead to a question of reliability.
The cost of validating a test kit’s performance on cadaveric blood was also a factor for manufacturers. The tissue banking market is a small one compared to blood donation, and the trials to prove new claims are expensive. However, AATB, with the Tissue Services playing a major role, helped the process along, by lobbying for participation in investigative new drug studies undertaken by both Chiron and Roche, who manufacture the kits for volunteer blood testing.
The action ensured the confidence in test results that additional research brings and the ongoing availability and improvements that competition can inspire.
Chiron’s tests have been licensed, and the licensing of Roche’s test kits is expected soon.
What’s Next?
Even before the March implementation, 80 percent of new donors from AATB-accredited tissue banks were being tested. A few, like Northwest Tissue Services, are currently testing inventory too, even though it is not mandated by AATB.
The first diseases for which NAT testing is available are HIV and HCV. HBV and West Nile virus are next on the list for NAT kit licensing for cadaveric blood testing. Those tests will also enhance the safety of tissue transplants by reducing the already-small chance of transmitting these infections.
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