The last few months have witnessed the unraveling of the remarkable life sciences company Theranos, culminating in the latest news that federal regulators may ban founder Elizabeth Holmes from the blood-testing industry for at least 2 years. The company is also facing a federal criminal investigation into whether it misled investors about its technology and company operations.

How has this widely acclaimed biomedical innovator fallen so far, so fast?

Theranos’ revolutionary claim that won over investors was that it could accurately run tests using a small amount of blood taken from a poke in the patient’s finger, instead of a syringe full from a needle stuck in a vein. The idea was that dozens of tests, such as cholesterol and thyroid hormone levels, could be run on a single, tiny blood sample.

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Theranos has had medical laboratory experts – including me – scratching their heads for some time. Having worked quite a bit in development of innovative medical tests, I knew what the company was promising just didn’t make a lot of sense.

Theranos’ much-hyped blood-testing technology

Theranos wowed investors, journalists and even groups like the Cleveland Clinic and Walgreens with what you might call an “iMedicine” vision of blood testing.

Basically, the idea was this. A few drops of blood from a fingertip are collected into a “nanotainer” collection tube and analyzed on the company’s proprietary machine, named after famed inventor Thomas Edison. How exactly the Edison devices work is unknown. But the claim was that many – possibly dozens – of tests could be run on those few drops of blood.

From a clinical perspective, this was always concerning, as such a shotgun approach to medical testing is actually very bad medicine. It is well-known that running numerous tests without symptoms or signs of disease invariably leads to false positive results.

Questions about the company’s technology came to a head in October. The Wall Street Journal alleged that Theranos might actually be performing the majority of its tests using traditional machines, the kind already in use in labs across the country, instead of its own much touted Edison devices. And then the FDA called the nanotainer an “uncleared medical device.” The company stopped using its signature collection tube, except in the single test that had been cleared by the FDA.

And, by the way, a machine capable of measuring many molecules on a drop of blood might seem like a breakthrough, unless you are someone familiar enough with life sciences technology to know that such capability has been invented numerous times. For instance, in my laboratory, we have a small handheld analyzer called an I-STAT. It can do 25 different tests on very small amounts of blood. It was developed more than 20 years ago and is commonplace today.

Blood from a finger isn’t same as blood from a vein

Let’s leave the technical issues aside for a moment and focus on those drops of blood from a fingertip.

The vast majority of FDA-approved medically important laboratory tests are based on blood taken from a vein, not from the finger. In fact, the package inserts for medical tests cleared by the FDA say something like “blood should be collected using standard venous blood collection techniques.”

To understand why that matters, let’s start with some simple physiology. The human body can be considered a series of compartments; the concentration of any given molecule in blood or tissue fluid may vary from one compartment to the next.

A small molecule, such as glucose, can move easily between these compartments, and any bodily fluid can generally be used to test its concentration. This is why testing blood sugar with a finger prick works.

But large, medically important molecules like proteins and lipids are not always found in uniform concentrations throughout the body. The composition of blood from finger pricks from the same person can vary, a problem that doesn’t happen in blood taken from a vein.

When you lance a fingertip, you get both blood and tissue fluid, and this means that the concentration of molecules may be different than if the blood sample comes from a vein.

The point is that blood taken from a finger would be considered another bodily fluid by the FDA, and any tests using finger prick blood would need to cleared by the FDA. According to news reports, at one time Theranos was seeking FDA clearances for as many as 120 tests. Even if its technology actually works, hundreds of FDA clearances would have required hundreds of clinical trials, a process that would have taken years to complete.

This article originally appeared on MPR