Nucleic Acid-Amplification
Testing Further Safeguards Nation's Blood Supply,
NHLBI Study Shows
State-of-the-art testing systems to screen donated
blood have improved the safety of the nation's blood
supply by preventing the transmission of potentially
deadly viruses, according to a new study funded by
the National Heart, Lung, and Blood Institute (NHLBI),
a component of the National Institutes of Health.
Nucleic acid-amplification testing (NAT) has helped
prevent the transmission of approximately five HIV-1
infections and 56 hepatitis C virus (HCV) infections
each year since it began being used in the United
States as an investigational screening test in mid-1999.
The study is published in the August 19 issue of the
New England Journal of Medicine.
"Risks to blood recipients from transfusion-transmitted
viruses such as HIV and hepatitis are already extremely
low, in part because of increased surveillance and
improved testing," said Barbara Alving, M.D.,
NHLBI acting director. "NAT enhances the safety
of the nation's blood supply by further reducing these
risks."
The study is the first and only one of its scope to
show the effectiveness of the NAT assay system nationally.
All major blood donation laboratories
in the United States participated, accounting for
more than 98 percent of tested blood donations. Many
organizations collaborated on the research, including
the American Red Cross, Blood Systems Research Institute,
America's Blood Centers, and the Food and Drug Administration
(FDA).
The study investigators analyzed all donations that
detected ribonucleic acid (RNA) from HIV-1 and HCV
by NAT between 1999 and 2002. The researchers then
looked to see which of these infected donations had
been missed by tests to detect viral antibodies or
antigens (proteins from the virus), the types of screening
previously used. They concluded that NAT reduced the
risk of HIV-1 and HCV infections associated with blood
transfusion to approximately 1 in 2 million blood
units. In comparison, other blood screening tests
are associated with rates of 1 in 1.5 million for
HIV-1 and 1 in 276,000 for HCV.
Blood donors have been tested for evidence of HIV infection
since 1985 and for evidence of HCV infection since
1990. Although increasingly sensitive tests to detect
HIV and HCV antibodies and HIV antigen were implemented
during the past decade, in rare instances infections
in donors have been missed. This is due to the "window
period" during which a donor can be infected
but still test negative on screening tests.
The NAT system, which was approved for use in 2002
by the FDA, can detect HIV and HCV infections in blood
donors earlier than other screening tests because
it detects viral genes rather than antibodies or antigens.
The appearance of antibodies requires time for the
donor to develop an immune response, and detection
of antigens requires time for a higher level of virus
to appear in the bloodstream.
With the use of NAT for HCV, the window period is reduced
by approximately 60 days (from an average of 70 days
to 10 days). For HIV-1, the average window period
with antibody is approximately 22 days. This is reduced
to approximately 11 days with the NAT tests used in
this study. The use of NAT has allowed blood banks
to discontinue two less effective screening tests
-- HIV-1 antigen testing and a test for a nonspecific
marker for HCV. Blood donations continue to be screened
with antibody tests for HIV, HCV, and other viruses,
which helps ensure the safety of the blood supply.
"NAT not only improves the safety of our already
safe blood supply, but the technology can be quickly
adapted to screen for emerging viruses," said
George Nemo, Ph.D., project officer of the study and
group leader of the Transfusion Medicine and Cell
Therapies Scientific Research Group at NHLBI.
For example, last year, screening for West Nile virus
was implemented in less than nine months with the
collaboration of the Centers for Disease Control and
Prevention and FDA and the rapid development of NAT
by manufacturers. Nearly 1,000 blood donors with West
Nile virus infection were identified by NAT and their
donations discarded.
"These findings also reflect an unprecedented,
national cooperative effort by blood collection centers,
industry, and federal agencies, which greatly enhances
the ability of blood donation centers to rapidly incorporate
new tests as needed," added Nemo. "This
collaboration also facilitates our ability to conduct
ongoing and timely surveillance of the nation's blood
supply."
NAT also makes it possible to identify persons in the
very early stages of HIV-1 and HCV infection. This
information may help the medical community better
understand risk factors associated with viral infection
and the natural history, disease progression, and
treatment for these infections.
One of the NAT systems used in the study was first
developed in the mid-1990s by Gen-Probe Incorporated,
in collaboration with Chiron Corporation, with support
for research and development provided by NHLBI. Results
of screening by the NAT system manufactured by Roche
Molecular Systems were also included in the study.
To interview Dr. Nemo about this study, please call
the NHLBI Communications Office at 301-496-4236.
NHLBI is part of the National Institutes of Health
(NIH), the Federal Government's primary agency for
biomedical and behavioral research. NIH is a component
of the U.S. Department of Health and Human Services.
NHLBI press releases and fact sheets can be found
online at www.nhlbi.nih.gov
(www.nhlbi.nih.gov) . |