Why More Blood Is Still Better When It Comes to Medical Tests

Getting enough data has historically been difficult when performing tests on small samples of blood.
November 18, 2015, 12:00pm

Revolutionizing the health care industry can be difficult, and no one knows that better than 31-year-old Elizabeth Holmes.

Founder of the embattled blood technology startup Theranos, Holmes claimed her company could run hundreds of tests on just a few drops of blood using proprietary technology—a claim that was skewered in October by the Wall Street Journal.

Whether or not Theranos' technology can do what it claims to do, the controversy has prompted discussion about the feasibility of using small finger-prick blood samples for a wide range of tests in lieu of intravenous draws.

Reduced costs and convenience are the main advantages, but getting enough data has historically been difficult when performing tests on small samples of blood.

According to Dr. Khosrow Adeli, a University of Toronto professor and senior scientist at the Hospital for Sick Children, smaller blood draws are usually preferred by most patients—and it's not hard to see why. It's less painful to take blood samples from a finger-prick than from a intravenous draw, which requires a medical professional to place tourniquet around a patient's arm, find a vein, and then insert a needle for blood collection.

There's also the matter of cost. Though lab costs, technician fees and hospital expenses vary, traditional intravenous draws require more blood and more time, explained Dr. Adeli. Finger-prick tests, on the other hand, "require less in-lab expertise, and reduce cost of labour, which could save a lot of money," he said.

But there is reason why finger-prick tests have not yet become the norm for most diagnoses, and it has to do with quality—or, more accurately, a lack thereof with smaller samples.

"In measuring anything in a sample, lets say blood or urine, our technology requires a certain amount of that substance to reliably detect it," said Dr. Vanessa Allen, chief of medical microbiology with Public Health Ontario.

"Tests that measure things like cholesterol, glucose, and electrolytes are fine, but small blood samples can only go so far," Dr. Adeli also explained—and there are only so many tests that can be run on a sample of that size.

"We have to repeat tests and replicate them over multiple runs to make sure they're done correctly [in labs]," Dr. Allen said. "We do all sorts of things that the public doesn't normally see."

It's possible that Theranos learned this the hard way. According to the Wall Street Journal, Theranos did the majority of its tests, not on its own proprietary Edison machines designed for small sample testing, but on more traditional machines that accepted larger samples. This required Theranos to dilute its finger-prick samples so that it could use them with the machines—but lab experts told the Wall Street Journal that this could increase the chance of inaccurate results.

It's important to note that some diagnostic equipment does dilute regular blood samples to some extent, says Cary Gunn, CEO of another finger prick blood test company called Genalyte, but when you dilute samples that are already very small you lower its concentration, therefore making it harder to accurately test.

Theranos did not return a request for comment.

None of these challenges have stopped other companies from attempting to shake up the industry in the ways Theranos has claimed. Graphene Frontiers and DNA Medical Institute are also looking for a solution to finger-prick testing's challenges, and US-based Genalyte claims to have made big strides with a system that can perform 128 tests on a single drop of blood in as little as 10 minutes.

By depositing a protein on each sensor's surface, Gunn and his team say they can program each of the chip's 128 sensors to perform a specific test. Each protein is designed to bind only to a particular blood component that sensor is configured to test.

"Our sensors are microscopic, literally 1000s of times smaller than older technologies, meaning we can work with much less blood and still deliver enough to the sensors to perform tests accurately," Gunn said. "A dozen of our sensors would fit on the end of a human hair. Since the sensor is so small the amount of material we need to make a measurement can be found in just a small fraction of one drop of blood."

For the moment, however, the commercialization of these alternative finger-prick tests is still some ways off. Genalyte's technology is only being used by medical researchers and trialed in physician offices, while DNA Medical Institute is undergoing its own ongoing clinical trials, alongside a pending patent, according to its website. But Dr. Allen is optimistic.

"I can see this being useful in the field where you can't test a large amount of blood—for instance, in our northern communities where it isn't easy is to send samples down south for testing or in developing countries," she said.

Yet, "quality [will] always needs to be embedded into any program whether it's point of care programs [for example, rapid HIV testing] or testing done in a lab pharmacy," Dr. Allen added. "You need to make sure the right results are given because it will cost more down the road if it's not accurate."