eyeing NAT’s impact
In the late ’90s,
it was called "exquisitely sensitive" and hailed as
a silver bullet in the nation’s long campaign to end the risk of
contracting HIV or HCV through blood transfusion. Nucleic acid amplification
testing looked as close as we could get to a test that would close
the window of viral transmission from donated blood—or at least
drastically decrease the risk of transmission.
In fact, that turns
out to be the trouble.
Rapidly adopted in
Europe for plasma derivatives, NAT took root in the United States
surprisingly quickly for all donations destined to become transfusible
components, despite its cost and immense logistical difficulties.
It became a routine part of blood bank testing in 1999, even though
it was still in clinical trials and licensing applications for the
assays were awaiting Food and Drug Administration approval.
Today, NAT testing
for HIV and HCV is performed on nearly 100 percent of U.S. blood
donations, and clinical trials have borne out the blood services
industry’s hopes for the technology. Over 24 million samples had
been NAT-tested for HIV and HCV as of November 2001. NAT caught
88 specimens that were positive for HCV RNA, and seven that tested
positive for HIV-1 RNA.
one in their right mind would be transfusing blood that hasn’t been
NAT-tested," says Ronald Sacher, MD, director of the Hoxworth
Blood Center at the University of Cincinnati and a member of CAP’s
Transfusion Medicine Resource Committee. "It’s the best test
we have, and there are no other tests that could in fact be as definitive
in terms of shortening the window period of infectivity."
Chiron Corp., which
distributes the Procleix System developed by Gen-Probe Inc., already
has 75 percent of the NAT-testing market for whole blood. So when
the Procleix System became the first to win approval from the FDA
last February for testing of whole blood donations, it may have
seemed anticlimactic. But licensing marks a milestone for NAT testing.
It means blood centers are effectively required to perform NAT testing
of blood donations (using either Chiron’s test or that of Roche
Diagnostics, which is awaiting FDA approval).
Licensing also means
blood centers can now label their products NAT-tested, manufacturers
can make a profit on their NAT tests, and blood centers will pay
a lot more for the assays. "Frankly, the primary impact of
licensing is cost," says Jim MacPherson, chief executive officer
of America’s Blood Centers. "When it is a research project,
the FDA requires that the manufacturers can only recover their costs.
They can’t make a profit or recoup their investment; they can only
charge exactly what the test costs. Now they can charge a profit."
Furthermore, NAT testing
will become more entrenched in the blood industry. "For the
foreseeable future, we’re going to be using NAT for any direct virus
test we use," MacPherson says.
NAT testing is tailor-made
for easing public anxiety over the blood supply. "With NAT
testing, we’ve been able to say to patients that, due to advances,
the risk of HIV when receiving banked blood is almost one in 2 million,"
says Katharine Downes, MD, associate director of blood banking and
transfusion medicine at University Hospitals of Cleveland and a
member of the College’s Transfusion Medicine Resource Committee.
"We’ve been able to allay a lot of fears. But the public’s
expectation for a zero-risk blood supply persists."
James AuBuchon, MD,
vice-chair of the CAP committee and professor and chairman of pathology
at Dartmouth-Hitchcock Medical Center, Lebanon, NH, specializes
in decision analyses and cost-effectiveness issues. He summarizes
the dilemma posed by NAT: "As the blood supply gets safer,
there are fewer cases of transmission remaining to be prevented
and therefore the cost-effectiveness of continued attempts to improve
safety will be very poor."
been true in the case of NAT," Dr. AuBuchon continues, "and
we will face the issue again when we consider moving from minipool
NAT to single-donation NAT. These steps will appear very desirable
to many. However, the morbidity and mortality caused by the residual
number of transmissions either before or after minipool NAT are
orders of magnitude smaller than other risks that patients face
Blood centers have
been screening for HIV since 1985 and for HCV since 1990. But pressure
to find more precise probes has never let up.
Blood centers actually
used NAT tests under extended investigational new drug exemptions
with the FDA, says Neil Gunn, vice president for marketing with
Chiron Blood Testing. "The FDA considers it an
important technology and it allowed extended INDs to be carried
out under a cost-recovery program."
NAT’s advantage is
that it detects viral genes rather than antibodies or antigens (proteins
for the virus). As a result, it can find viruses earlier. "Surface
antigen takes a period of time to develop. The beauty of NAT is
it doesn’t wait. It actually searches directly for the viral RNA
or DNA, so you can detect its presence much earlier," Gunn
While Chiron uses
a process called transcription-mediated amplification for its NAT
testing, and Roche uses polymerase chain reaction, "at the
end of the day the two tests are identical," MacPherson says
In fact, NAT testing
has slashed the window between viral infection and the ability of
an assay to detect the virus. The window for HCV fell from 82 to
25 days, and the average HIV-1 window fell to 12 (compared
a 16-day window with antigen testing).
advantage of this test has been with hepatitis C, as one would predict
because of its longer window period," says Laurence Sherman,
MD, JD, co-chair of the Transfusion Medicine ResourceCommittee and
professor emeritus of pathology at Northwestern Medical School in
Chicago. "The impact was less for HIV, because with the most
recent tests that had gone into use for HIV, one was already looking
directly for the virus rather than just the antibody."
But those tests will
soon recede into the background. "The approval of the Chiron/Gen-Probe
test allows the removal of the requirement for p24 testing for HIV,"
Gunn says, noting that it is one of the unique features of the FDA’s
licensing of Chiron’s NAT test. "Under our package insert,
blood centers could actually eliminate p24 testing for HIV. The
major rationale, the FDA said, is that the NAT assays should be
able to identify all known
There is pressure
from the American Red Cross and America’s Blood Centers to move
forward on eliminating p24, Dr. Sherman says: "There’s been
a lot of interest in doing that, particularly since the cost of
blood products has risen much more rapidly than other things in
the health care arena—let alone the CPI. From a laboratory standpoint,
the increase in the cost of blood products is much greater than
The p24 antigen phase-out
could at least trim possible enormous costs for blood centers as
NAT testing widens its scope. "Our hospitals don’t like it,
of course," Buff Mair, MD, medical director of Florida Blood
Services, St. Petersburg, and a member of the CAP transfusion medicine
committee, says. "We try to absorb the extra costs as much
as possible, but ultimately as the test gets more sophisticated
and more expensive, it gets passed on to the consumer—which is the
Most blood centers
expect that Roche Diagnostics’ NAT tests for HIV and HCV will also
get FDA approval next year. "We are on a fast track,"
says Patrick Aquilino, Roche’s marketing manager for blood screening.
The Roche assays are used to screen about 25 percent of the U.S.
blood supply. "We are making every effort to facilitate approval
of our applications with the FDA," Aquilino says.
only Chiron will be able to make a profit for the time being, blood
centers won’t be able to use the Roche test to save money. "Roche
has been charging a royalty ever since it settled its patent dispute
with Chiron, and the royalty went up significantly after the Chiron
test was licensed," MacPherson explains. "And although
that is a profit to Chiron, it is a cost to Roche."
Licensing will also
increase the impact of NAT testing on blood safety. Although U.S.
blood centers almost universally performed NAT testing while Chiron’s
license was pending, they did so under "Phase 1" conditions
of the investigational new drug exemption—which meant that blood
components were sometimes not quarantined. They could be issued,
and potentially transfused, before the NAT results became available.
Michael P. Busch,
MD, PhD, professor of laboratory medicine and vice president of
research and scientific affairs for Blood Systems, the second largest
blood collection organization in the U.S., reported in 2000 that
each positive donation could well have infected two to three recipients,
but, as it turned out, only one NAT-positive component was transfused.
Dr. Sherman notes
that in addition to the lack of quarantine for new blood components,
often frozen products such as plasma and cryoprecipitate that were
drawn before blood centers or hospitals started NAT testing, and
that were still on their shelves, weren’t exchanged for test-negative
products. "In late 1999, at an FDA workshop the majority of
institutions had not exchanged frozen products," he says.
The FDA had set a
target date of mid-2000 for everyone to treat NAT tests the same
as licensed tests, even though they couldn’t label it, Dr. Sherman
adds. He believes very few people have been transfused with these
products, and that in fact the pre-existing systems and tests were
quite good. "The issue really was if you’re doing it, and charging
for it—and virtually everybody is—then the people you’re charging
ought to be getting a test-negative product," Dr. Sherman says.
The CAP Transfusion
Medicine Resource Committee only recently completed plans for a
proficiency test for NAT, which is scheduled for introduction early
in 2003. "This is not an easy test," Dr. Sherman says.
"CAP’s microbiology committee has been doing a proficiency
Survey for viral load NAT testing—measuring how many HIV virions
are in a person who’s undergoing treatment—for some time. And it’s
been apparent from the proficiency tests there that the tests aren’t
as precise as one would like. We spent a fair amount of time developing
a Survey for blood donor centers proficiency testing for NAT as
well. It really took longer than we expected, but we finally have
it and it’s in the catalog."
One practical problem
of developing a proficiency test, says Dr. Sherman, was that "CAP
to the greatest extent possible does not ship infectious material,
unless we’re sending something to see if you can grow a bacteria."
Policy and plasma
NAT testing’s widespread
use in whole blood has been closely tied to its use in the plasma
industry—even though different methods and technologies are used
to perform the assays. Laboratory Corporation of America Holdings
was first to be FDA licensed for NAT testing. LabCorp’s test is
a screening test for plasma, which differs from whole blood in several
major ways. Plasma has a number of different uses, including its
use as a raw material for the manufacture of clotting factors for
hemophiliacs and immune globulin, whereas whole blood is used primarily
for surgeries and emergencies in which large quantities of blood
cells are lost. The key difference is perishability.
Andrew Conrad, PhD,
chief scientific officer of LabCorp’s National Genetics Institute,
notes that "plasma is very, very stable, but whole blood isn’t."
Whole blood is good for a few weeks and then discarded, whereas
plasma can remain frozen for use for years. The whole blood tests
are done quickly on individual samples, or in most cases small pools,
to make the whole blood available as soon as possible. "Plasma
screening tests are done on larger pools," Dr. Conrad says,
because plasma collections can be held in storage, allowing for
more complex resolution algorithms that take more time and allow
for larger pools.
"A small blood
bank could wait weeks to get pools of more than 500 samples,"
Dr. Conrad says, making the whole blood essentially unusable by
the time it gets tested. Plasma, however, can be frozen and held
as long as needed to accumulate the desired number of samples for
testing. The basic ideas for testing whole blood and plasma are
similar, but, Dr. Conrad notes, "plasma has a bit of a luxury
in that the time pressures aren’t the same." Economies of scale
are another advantage deriving from plasma’s lower perishability.
Whole blood tests need a system that can be put out in many locations,
whereas a central plasma testing laboratory can get huge shipments
in to test.
NAT tests for plasma,
in fact, are sometimes used as confirmatory tests when NAT tests
of whole blood are positive. For all whole blood that uses NAT tests,
a positive result is confirmed with an independent, different test.
How can the plasma
test be used for whole blood? Once the test result on whole blood
is positive, the blood cannot be used—so time is no longer of the
In addition, although
the blood cells in whole blood are perishable, the whole blood can
be spun and the plasma recovered. "Here is where the two worlds
meet," Dr. Conrad says.
Steven H. Kleinman,
MD, a pathologist with the University of British Columbia in Vancouver,
noted at a recent FDA Blood Products Advisory Committee meeting
that the source plasma industry sets a standard and influences the
whole blood industry, in a way that has trumped FDA regulation.
Indeed, Dr. Sherman
points out, the European Union’s requirement that all plasma shipped
there be NAT-tested jump-started the near-universal adoption of
the technology in the United States. "It was part of the reason
for getting it up and running. A lot of blood centers here ship
plasma to Europe, and the EU was not accepting any plasma that wasn’t
NAT-tested after July 1, 1999," Dr. Sherman says.
Union was quicker to jump on this requirement," Dr. Sacher
agrees, although he downplays the EU’s requirement as an incentive
for U.S. blood centers to adopt NAT testing. He notes that part
of the EU’s alacrity stemmed from the inactivity of many European
blood supply officials in the early part of the AIDS epidemic; in
some countries directors of testing were criminally indicted.
However, Europe has
not wholeheartedly embraced NAT for whole blood donations. While
Germany and France require it, the United Kingdom currently only
tests for HCV with NAT. "It does not conduct HIV NAT testing
because it believes that the cases it would find are relatively
low in number," Chiron’s Gunn says.
The UK is not alone
in its concern about the price of NAT testing. There has been a
huge uproar over pricing in Europe, and it has spawned major litigation,
Dr. Busch notes: "The Europeans developed these assays themselves
and brought them up before we did; then Roche and Chiron are saying
in addition to $1 or $2 per donation, give us $5."
Gunn suggests that NAT testing is worth the extra cost, in part because it
can improve both the safety and the availability of blood products. "All
too frequently there are blood shortages, and we want to work with the blood
industry to help reduce the impact of these," Gunn says.
A web of patent rights
has complicated the availability and development of NAT testing.
Roche Diagnostics has a patent on the PCR technology used for nucleic
acid testing. "That’s why Gen-Probe/ Chiron had to come up
with something different and it developed the TMA approach,"
Dr. AuBuchon says.
However, Chiron, which
cloned and first identified HCV as the cause of transfusion-related
non-A, non-B hepatitis, as it was then called, has granted nonexclusive
licenses to its HCV technology to many of the large diagnostics
companies. It recently settled a patent dispute with Roche over
this technology with an agreement that Roche would pay tens of millions
of dollars to Chiron and pass through future royalties on the HCV
test to Roche’s customers.
means that Chiron has a monopoly on NAT testing for HCV, Dr. Busch
explains, and it licenses the technology to other companies such
as Roche. Chiron charges a royalty per donation even though the
samples are pooled for testing—which Dr. Busch considers a pricing
structure that artificially "skews the potential decision to
move the nation from pooled to individual-donation testing."
"They are charging
a $5 royalty no matter whether the test samples are in pools of
100s or singles," Dr. Busch says. "As a result, moving
from minipool to single-unit testing doesn’t drive prices up dramatically.
It may only increase them marginally." He predicts that costs
will remain high because of such patent issues. "To my mind,
we’ve seen prices go up progressively more than anticipated, so
that’s the end of discussion of the so-called economy concept that
with multiplexed assays you’d save money."
Despite these factors,
competition in NAT testing survives. "We worked very, very
hard to make sure both companies stayed in business," says
MacPherson. "We did not want to see Roche forced out because
of the patent dispute, so we encouraged both companies to settle,
and they did." Competition between companies is almost always
good, he believes, because it stimulates improvement. In this case,
"Chironthrough its partner Gen-Probe brings innovation, but
we also know that Roche has the world market in NAT testing, and
we wanted both," MacPherson says.
Drs. Busch and AuBuchon stress that to some extent the attention focused on
NAT could profitably shift to other, more cost-effective measures. Dr. AuBuchon
says, "The two major risks that transfusion recipients face today are incompatibility,
which in red cells causes acute hemolytic transfusion reaction, and, for platelet
recipients, bacterial contamination. Each of these appears to cause between
one and two dozen deaths in the U.S. annually—far outpacing the frequency of
HIV [one per 2 million]."
vs. pooled testing
The most contentious
debate is now over individual-donation testing, which is being seriously
considered because, despite the sensitivity of NAT, a few infections
still escape detection when samples are pooled.
"The issue is
really one of dilution," Dr. AuBuchon says. "In a minipool
as currently set up in the U.S., between 16 and 24 units are tested
simultaneously. Statistically, only one is going to be an infected
unit. Therefore HIV in that single hot sample is going to be diluted
by the negative members of the pool, and if the concentration of
the genome is near the detection level, it may be diluted below
the detection level."
That possibility is
more than theoretical. At a Sept. 12 meeting of the Blood Products
Advisory Committee, the FDA announced that three cases of HIV transmission
during the window period have occurred since the introduction of
NAT. Indira Hewlett, PhD, director of emerging and transfusion-related
diseases at the FDA, said at the meeting, "It is FDA’s current
intention that when feasible and when the appropriate platforms
become available, ID [individual donation]-NAT would eventually
be implemented for mass screening of donors."
"Things are still
very dynamic," says Dr. Busch. "Unfortunately there have
been a couple of breakthrough transmissions where the minipool actually
didn’t detect an infectious donor." As a result, some blood
centers are going to ID testing—a trend driven mostly by the military,
which tests only 40 to 50 samples a day in its laboratories. The
Oklahoma Blood Center, a frequent early adopter of new screening
technology, has also announced it will do individual-donation NAT
site is telling us if an individual center said, ’Look, we want
individual NAT on our donations,’ they could actually do that, and
be charged accordingly," says Francis R. Rodwig Jr., MD, chairman
of pathology and laboratory medicine at the Ochsner Clinic Foundation
in New Orleans and member of the CAP transfusion committee. "They’re
still working the price out, but it would be a lot more expensive,
and it’s a big concern because we know there’s a lag between increased
charges and increased reimbursement."
Dr. Busch is similarly skeptical because of the extremely high cost of ID
testing compared with the gains. "The relative benefit of ID-NAT when compared
with minipool NAT is very small because the ramp-up phase of viremia is logarithmic,
with a double time of 21.5 hours," he says.
While the American
Red Cross has said it is considering an intermediate reduction of
pool size, which would partially address the dilution problem, most
blood center officials as well as the FDA consider ID unfeasible
without automation—and the industry is only halfway there.
improved on the traditional PCR testing laboratory, Dr. Rodwig says:
"Traditional PCR was a person sitting in a laboratory with
a pipette, doing hours and hours of delicate testing. Now the samples
are collected and pooled, they go through an analyzer, and the results
are spit out at the end."
But fears of cross-contamination,
possibly causing the wrong DNA to be amplified, make any process
of PCR difficult to automate. Referring to the extraction steps
in the Roche test and the extensive manual pipetting required for
the amplification phase of the Chiron test, Celso Bianco, MD, executive
vice president of America’s Blood Centers, urged Gen-Probe, Chiron,
and Roche to hasten their development of automated instrumentation.
Chiron’s test is a
semiautomated system, Gunn says. "A large amount of it is automated
but some of the individual steps are quite manual, and we are looking
to automate those as we go forward over the next couple of years,
with a view toward full automation in the mid-term."
Chiron has been promoting
single-unit testing to small labs, Dr. Busch says, because it can
give them a competitive advantage over large labs: "Thelarger
megalabs like ours or the Red Cross clearly can’t go to single-unit
until there’s appropriate automation."
"It’s not so
much a cost issue as having to increase staff three- or fourfold,
when most can’t even hire enough staff to keep afloat now,"
says Dr. Busch. "The companies themselves would be the first
to admit that anyone that tests over 100,000 donations a year would
be pushed to the edge if they tried to turn around test results
in a timely fashion."
Dr. Mair agrees. "The logistics of single-donation testing are complicated
because NAT testing is not automated." At Florida Blood Services, which
performs 825,000 NAT tests per year, one technologist can process 2,816 samples
with eight to 10 hours turnaround time, if they are negative; positive tests
require additional testing. "It does require hands-on tech time, and there’s
a nationwide shortage of techs," she says.
Hoxworth Blood Center’s
Dr. Sacher says three cases have been reported in the past yearin
which the NAT test was negative but HIV was transmitted. "So
even though the window period for HIV is probably now about six
to seven days, there’s still the potential of a donor who has the
virus in their system not being detected by NAT," he says.
believes, blood centers will go to single-donor NAT. "There’s
a pretty small clinical advantage to single-donation testing for
HCV. You’ll only close the window by a couple of days because the
virus ramp-up is so fast," he says. "With HIV you can
close the window maybe another seven to 10 days by going to individual
testing. The controversy is whether it’s worth it to multiply the
workload, let alone the cost, by 16 times to pick up one case of
HIV per year."
Dr. Busch is skeptical
the tradeoff is warranted: "Our analyses would suggest we’d
probably pick up three additional HIV- and three additional HCV-infected
donors per year in this country, out of 13 million donors, that
are currently missed by minipool and could be detected by single-unit.
The problem is it will cost us $100 million to pick thoseup."
The FDA said in September
that the currently licensed platform "requires upgrades including
automated sample preparation, reagent preparation, etc., to maximize
its efficiency for high volume use for ID-NAT. These upgrades and
the necessary regulatory submissions for their approval will require
time. Therefore, although ID-NAT may be technically feasible, it
may not be operationally so at the present time."
The question of hepatitis
B NAT testing has generated similar debate. There is no HBV NAT
test yet in the United States, but this past summer Roche began
clinical trials of its Cobas Ampliscreen HBV test. The Japanese
Red Cross is already performing HBV NAT testing to screen blood
donations as part of Roche’s triplex AmpliNAT assay. Chiron has
also developed a triplex test, set to begin clinical trials in Europe
in 2003, that looks for HBV as well as HCV and HIV.
The market is unquestionably
there. "Around the world there are probably 300 million people
with hepatitis B," Gunn points out. "The demand for an
HBV NAT test will come from its prevalence within the blood donor
population, and we’ll get a much better estimation of that in 2003."
Antigen tests already in place are less sensitive than NAT would
be, he adds, and preliminary data suggest the HBV window can be
reduced by 20 to 30 days over current assays.
However, Dr. AuBuchon
says, "Hepatitis B causes serious consequences or long-term
chronic complications much less frequently than HCV.
So the advantage of adding the HBV primers to NAT will be relatively
limited." In addition, the low level of viremia associated
with HBV at the beginning of infection is a related drawback of
NAT testing for the virus.
Says Dr. Downes: "There
is also a very slow doubling rate of HBV, about every three days,
which makes the amount of HBV DNA present in the pooled sample much
lower than in HIV and HCV in the early part of infection. So performing
NAT on HBV pooled samples appears to be less useful."
Other NAT tests likely to be adopted are for hepatitis A and parvovirus B19,
although there is little consensus that they are urgently needed for blood safety.
"The reality is people who collect whole blood are having to do things
that don’t make sense in the whole blood sector, and do make sense in the source
plasma sector, and it may be because they want to be competitive in the market
for their fractionated products," Dr. Kleinman says. "I think everybody
should recognize that because of safety concerns in the source plasma industry,
the whole blood industry has implemented a series of tests, some of which would
have been implemented anyway, like HCV and HIV NAT perhaps, but others of which,
like parvovirus B19 and HAV NAT, probably have no value for blood donors and
probably no value for the final products."
a new threat
West Nile virus is
the latest potential candidate for detection by NAT assay. In September,
the Centers for Disease Control and Prevention confirmed that four
recipients of organ transplants from a single donor had contracted
West Nile. The organ donor, who also turned out to be positive,
had been transfused with blood from more than 60 blood donors.
West Nile has been
a particular concern in Louisiana, which has had a large number
of cases and deaths. Ochsner Clinic Foundation’s Dr. Rodwig says
there has been a lot of uncertainty about testing because there
has never been a case definitively associated with blood transfusion.
"It would be impossible to quickly develop a NAT test,"
he says. "Of course you could do an antibody test—but we don’t
know if that would just unnecessarily screen out donors."
The transfusion link
is still theoretical, but the CDC and FDA said Sept. 19 that West
Nile virus can survive in some blood products and can "probably"
be passed through blood transfusions.
As a result, federal
officials are increasingly convinced that they need to quickly develop
a screening test to protect supplies in blood banks. NAT testing,
in fact, will be well suited for West Nile if it proves cost-effective.
Since peak viremia occurs one or two days before the onset of illness,
antibody tests would not be useful as blood donor screens.
Public alarm over
the polio-like effects of West Nile all but ensures that NAT testing
for the virus will eventually be required. And many blood experts
like Dr. AuBuchon caution that perspective, not alarm, is needed
to keep blood policy cost-effective.
is a versatile technology that will allow us to expand our oversight
of the blood supply against new threats," Dr. AuBuchon says.
"But I would not want us to forget that there are other, much
larger problems than viral transmission."
Anne Paxton is a writer in Seattle