NUCLEIC ACID AMPLIFICATON TESTING (NAT)
Arell Shapiro, M.D., LifeSource Blood Services
Technology such as polymerase chain reaction (PCR) has enabled direct
detection of a variety of pathogens from a variety of clinical samples. This technology
has recently been applied to blood donor screening under three large research protocols in
the United States. Central Blood Bank and LifeSource Blood Centers will be testing donors for
HCV nucleic acid beginning this month under IND (FDA-approved, Investigational New
Drug application). In August, screening for HIV nucleic acid is anticipated
to begin. It is predicted that the addition of NAT screening will incrementally
improve the blood safety margin by decreasing the "window" period, when
conventional tests are unable to detect virus. It has been estimated that NAT
testing will decrease the window period for HCV from the current 70-80 days to 10 - 30
days; and HIV from the current 16 days to 10 days. The risk of HCV transmission is
expected to decline by approximately 80% from 1:103,000 to 1:500,000 - 1:1,000,000.
It is important to emphasize that the efficacy of NAT testing is under study.
It has long been the goal to have a zero-risk blood supply. As a
result, tools such as PCR have become available to Blood Centers for donor screening and
they are being applied as permitted by the FDA. The European Blood regulatory agency
is requiring that all plasma for further manufacture be tested for HCV RNA by NAT by July
The complexity of NAT and the lack of automated testing equipment and
reagents make it impossible to test donations singly. NAT testing will be performed
on small pools of donor samples (24). The system for testing is designed to have a
specified sensitivity necessary to make this screening effective.
THE HCV RNA TESTING STUDY
This clinical study is a prospective multi-center study to determine
whether the addition of a Nucleic Acid Amplification Test (NAT) for the presence of HCV
RNA in plasma pools prepared from volunteer blood donations detects
more potentially infectious units than the testing of individual donations with FDA
licensed serological tests alone.1 It will also evaluate the ability of blood centers to perform
pooling and testing for blood components with short expiration dates (e.g. platelets) in a
timely manner. Until this latter can be established, blood centers may release
cellular blood components (whole blood, red cells and platelets) based solely on the
results of the FDA approved anti-HCV test procedures (Phase 1) of this clinical study.
In Phase 2, Blood Centers will only release blood products that have both NAT and
serologic negative results. Because this investigational donor screening study is
under IND, blood units cannot be labeled or marked as tested or untested by NAT.
The study requires testing of samples from all volunteer donors.
Donor samples are tested at a central testing center. NAT results are sent back to
the Collection center so NAT test negative units can be released. Stringent
requirements for donor sample storage assure that testing will accurately reflect the
donors HCV status.
ITxM/LifeSource will be performing the NAT testing for Central Blood Bank and LifeSource.
A special area has been created to assure that the testing is accurately performed
and free of contamination. Pools of 24 donor samples, the Primary Pool, is created
and tested. If the pool is negative, all members of that pool are considered NAT
negative. If the Primary Pool is positive, the members of that pool are retested in
four groups of 6 donor samples (Secondary Pools). If a multiple secondary pool
is/are positive, the individual members of that pool(s) will be tested. Secondary
pools that test negative are considered NAT negative. Resolution of positives is to
the individual donor or donors. Discordant results between a positive NAT result and
negative HCV antibody serologic testing will trigger follow-up testing of the donor and
In August, the addition of NAT testing for HIV is planned. The duration
of that clinical study is thought to be 12-18 months.
Hospitals are integrally involved in this process, as they will be
facing a period of time where their inventories will contain both NAT tested and NAT
untested blood. Hospital issues include: whether or not consent from
recipient/patients of NAT untested blood is needed, costs of this additional testing
(approximately $6.50 per unit), and coping with a mixed inventory.
Hospitals are encouraged to "consider the usefulness of including
a statement that addresses the issue of NAT in their transfusion informed consent
process." 2 Because current FDA regulations allow institutions providing
products and services under an IND protocol to recover reasonable costs for the product or
service, Blood Centers are increasing fees to recover the cost of this testing. The AABB is seeking support for increasing reimbursements from
third party payors for this new safety initiative at the federal level.3 However, the
primary concern voiced seems to be the possibility that a NAT untested unit, released in
Phase 1, may test NAT positive and trigger recipient notification. That possibility
is very low, as donors who are RNA positive and HCV antibody negative may represent only 1
in 100,000 donors. As well, the ITxM Blood Centers are committed to only releasing
NAT tested units unless severe product shortages arise. In these cases, it would be
imprudent to hold blood acceptable by FDA licensed tests and donor screening processes
because NAT results were not available.
NAT HCV RNA screening to improve the safety of the blood supply has been implemented.
NAT does not add risk to transfusion; therefore issues about informed consent
should be made by hospitals via standard mechanisms for making ethically based decisions,
such as Transfusion Committees, Ethics Committees or IRBs. 3 Three large
multi-center research studies are examining the efficacy and feasibility of this type of
sophisticated testing of pooled donor samples. The IND process requires rigid
conformance to the details of the clinical studies and prohibits "claims of
additional safety" and labeling units as "NAT tested". This move
toward improvements in safety create ethical, logistic and financial issues for hospitals.
Investigators Brochure "A Prospective Study to Evaluate the Testing of
Plasma Pools from Voluntary Blood Donations for the Presence of HCV RNA", Roche
Molecular Systems, Inc., Somerville, N.J.
American Association of Blood Banks
Association Bulletin #99-3, "NAT Implementation", February 8, 1999
American Association of Blood Banks
Association Bulletin #99-6, "NAT Implementation - Additional Guidelines",
March 10, 1999
Copyright © 1999, Institute For
|For questions regarding the NAT
Testing Program, please contact the Blood Center Physicians at
(412) 209-7320 (CBB) or at (847) 803-7825 (LifeSource).
Copies of the Transfusion Medicine Update can be obtained by
contacting Deborah Small (412) 209-7320
Visit our web page for information and previous issues of the TMU newsletter at www.itxm.org