The Non-invasive Problem

One of the ways to make a non-invasive blood glucose meter that is most attractive to researchers is optical technology. It has the promise of being less painful and more affordable than our current blood glucose meters.

In the news earlier this month is the work that a team at the University of Southern California’s Viterbi School of Engineering has high hopes for. A correspondent was kind enough to bring to my attention a December 28 article by Prachi Patel-Predd about a “New Optical Glucose Sensor” in Technology Review from the esteemed Massachusetts Institute of Technology.

Led by Gerald Loeb, a professor of biomedical engineering there, the team is measuring the change in fluorescent emissions that occurs when glucose binds to certain molecules. The sensor is a tiny optical fiber that could be implanted in the skin of people with diabetes.

Dr. Loeb says that a portable analyzer will shine ultraviolet light into the free end of the fiber, measure the fluorescence, and tell us our blood glucose level. He says that we should be able to leave this little fiber inside our skin for a few months at a time. When they implanted the fiber in pigs for up to three months, the pigs didn’t show any inflammation or even complain.

You can read more of the technical details in the article that I link above. But note that implanting a fiber, no matter how small, under our skin sort of stretches the definition of the term non-invasive.

And worse, something very much like it has been tried before without any success at least so far. To evaluate this and other proposed non-invasive solutions I always turn to the leading expert on non-invasive blood glucose technology.

He is John Smith. When he retired the from LifeScan, which makes the well-known OneTouch meters, he was the company’s chief scientific officer. He came out of retirement the first time to head Fovi Optics Inc. in Santa Clara, California, which tried in vain to develop non-invasive optical blood glucose meters.

John then came out of retirement again, this time to try something totally different – to make wine. But he keeps up-to-date with all developments that might some day lead to a non-invasive meter, and wrote a great book about it that is available as a PDF on my website.

Dr. Loeb’s team and others working on non-invasive optical sensors face what John calls the ‘foreign body problem.” Lots of companies and researchers previously investigated the use of a “reporter molecule” placed just under the skin, John says. They include Sensor Technologies, Sensors for Medicine and Science, Gerard Coté, BioPeak, Minimed, Glumetrics, Becton-Dickinson, Precisense, Minimed, Motorola, andArgose.

The idea sounds great – just a tattoo or minor injection under the skin. Then a sensing device can read the amount of glucose by shining light through the skin and measuring the response. But it’s really difficult to do.

“The practical complications are similar to those that have plagued investigators who have tried to develop long-lived in-dwelling sensors,” John says. “Any thing inserted into the body that is not rejected by the immune system will be incorporated by the organism surrounding it with a coating of protein – the foreign body response – with two problems for glucose measurement: It can both reduce the access of glucose to the sensing material, or it can decrease the amount of light that passes into it or is transmitted back out of the reporter.

“In every case so far, the result has been that the lifetime of the material in the body is limited, and the accuracy degrades over the period of a few days. And when a ‘noninvasive’ measurement device requires frequent recalibration using an invasive device, it quickly loses its appeal to the user. A further complication is introduced by the variable reflectance of skin, requiring precise alignment between the reader and to skin area to be read. It’s easy to underestimate during the early, enthusiastic years, but the practical complications of a requirement like this need to be considered when assessing how well patients would be able to use a device in the home, or how long they would continue to use it.”

It would be great if the University of Southern California approach would work. But John and I are afraid that with more experience this technology will be added to the scrap heap of history.

This article is based on an earlier version of my article published by HealthCentral.