Nano-bio-chips
like this one made of silicon (in blue) can be
used to test saliva for characteristics of heart
disease
Photo credit: Glen Simmons
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Pinpointing patients who've just
suffered a heart attack may soon be as simple as asking
them to spit into a tube. Transfer the saliva onto a
lab card with integrated bio-chip, push that card into
an analyser — and voilà, 15 minutes later
you have your answer. The test is quick and painless
and could be administered in the ambulance, yielding
a result even before the patient arrives at the hospital.
"Right now, an EKG is the first
thing that's done when you suspect a heart attack, but
it misses 25 to 50% of MI patients," explains John McDevitt,
PhD, one of the lead scientists investigating this new
technology at the University of Texas. "After the EKG,
the next step is a blood-based test, for which the patient
needs to wait in line, etc. All said and done, it often
takes between 60 and 90 minutes for the results to come
back." If the person has indeed suffered a heart attack,
the 'golden hour' — the time slot when treatment
is most crucial — has been squandered.
That's where the saliva test may
make a huge difference. As a companion to the EKG, ie
administered early on, it could greatly reduce the number
of missed MIs upstream in the diagnostic pathway. Explains
Dr McDevitt: "In our recent trial, the EKG alone missed
33% of heart attack patients. When it was combined with
the spit test, that number went down to 3%."
SAME,
BUT DIFFERENT
The principle behind the test is similar to that of
current serum-based assays measuring cardiac markers
such as CK-MB, myoglobin and troponin I. It analyses
proteins present in saliva that correspond to heart
damage in roughly the same way as the markers used in
blood tests. From an initial 109 proteins they were
looking at, Dr McDevitt and his colleagues have narrowed
it down quite a bit: "Four proteins can shoot up an
answer that's nearly equivalent to the FDA-approved
serum-based test."
A definitive plus of the saliva
test is its ease of use. While patients currently still
have to spit into a tube, it's quite possible that in
the future, they may be able to spit directly onto the
lab card — the researchers are still figuring out
what makes the most sense in this respect. For the healthcare
provider, the test is simple, quick and convenient.
The lab card has the same format as a credit card, and
when asked about the size of the analyser, Dr McDevitt
cheerfully reports that "it's about half the size of
a toaster." In other words, it's very transportable
and should fit easily into any ambulance.
TEST
OF TIME
So how long until the spit test hits the market? Right
now, the technology is still in the clinical testing
phase, so it'll likely be another two to five years
before it becomes commercially available. But the good
news is that the lab card for acute MI is only the beginning
— there's lots more in the pipeline. For instance,
the researchers are also working on a bio-chip that
assesses the risk of a future heart attack or other
cardiovascular event. "This kind of chip could be used
at the GP's office or pharmacy to provide direct feedback
to patients on how lifestyle changes affect their health.
There's a score they can look at to see how they're
doing," explains Dr McDevitt. He goes on to say that
his group is currently talking to dentists to see whether
the test could be combined with dental exams: "The dentist
appointment is the most regular check-up that people
go to, often twice a year. But not everybody goes for
their yearly physical." Such regular monitoring would
allow patients and healthcare providers to keep an eye
on the progression of risk factors.
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