For many diabetics, the unpleasant chore of drawing blood several times a day in order to check blood glucose levels is a part of life. Efforts to develop devices that can test blood glucose without the need to repeatedly prick fingers have faltered thus far due to questions about accuracy as well as complaints about skin irritation. One company is hoping to solve these problems with a biochemical sensor that adheres to the skin like a bandage and sends continuous blood glucose readings to a handheld wireless device.



A proper blood glucose level is essential to one's health, especially for diabetics, whose bodies either produce none or too little of the glucose-regulating hormone insulin. Because high blood glucose levels can lead to a long list of serious health problems—glaucoma, nerve damage and heart disease, to name a few—diabetics must test their glucose levels several times each day, typically using a lancing device to pierce a fingertip and draw blood.



Echo Therapeutics, based in Franklin, Mass., is developing a wireless, needle-free transdermal continuous glucose monitoring system called Symphony tCGM for diabetics (there are nearly 24 million in the U.S.) and for use in hospital critical care units.



Symphony tCGM has three basic components: a Prelude SkinPrep System—a device roughly the size and shape of an electric nose-hair clipper—that shaves away the dead outermost surface of the skin (microdermabrasion), leaving a dime-size spot; a glucose biosensor that is applied there (generally on the chest or upper back); and a wireless handheld device that reads glucose levels from the biosensor.



As the Prelude removes skin and hair that could interfere with the biosensor's reading, it passes tiny electric pulses into the skin, says Echo Therapeutics chairman and CEO Patrick Mooney. Based on the response to these pulses, the Prelude can determine when it has reached live underlying skin cells that allow the biosensor to provide a more accurate reading. The patient then applies the disk-shaped biosensor to the patch of skin prepped by the Prelude. The membrane on the biosensor's surface detects glucose as it diffuses out of the body's capillaries. The sensor contains an enzyme that reacts with the glucose and relays the indication as an electric signal. The impulse passes wirelessly to a handheld device, which records the information and monitors the readings. Each sensor can be used for two days before being replaced by a fresh one, and then either used in the same spot or another Prelude-treated location.



Tufts Medical Center in Boston spent several years as a clinical site testing Echo's Symphony tCGM. "We frequently during surgery take blood samples for instantaneous testing" of blood glucose levels, regardless of whether the patient is diabetic, says Michael England, the center's chief of adult cardiac anesthesia. Continuous monitoring is particularly important during surgery because patient insulin levels vary. "Regular insulin we give people during surgery could take 45 minutes to an hour to take effect," he says.



England co-authored (along with three Echo researchers) a July 2008 study in the Journal of Diabetes Science and Technology indicating the accuracy of Symphony's blood glucose measurements was comparable with the more common practice of drawing and testing blood samples. This finding was consistent with the results of a Symphony tCGM study that Echo announced in November. Using about 900 Symphony tCGM glucose readings paired with reference blood glucose measurements (taken using blood samples), Echo claimed its technology was 97 percent accurate.



Beyond its potential impact on surgery and daily diabetes maintenance, England says continuous glucose monitoring might help doctors better understand insulin and how it works in the body. About 50 million people worldwide use insulin, according to the Joslin Diabetes Center in Boston.



The only "noninvasive" glucose meter to have received U.S. Food and Drug Administration (FDA) approval is no longer on the market. In 2001 Cygnus, Inc., won FDA approval for its GlucoWatch, which was worn like a wristwatch and designed to be used in conjunction with conventional blood testing to track trends and patterns in a patient's glucose levels. The GlucoWatch administered a small electrical charge into the wrist to bring glucose to the skin surface where it could be measured every 10 minutes. The device, however, was discontinued in 2007 after complaints about its accuracy and that it caused skin irritation in some users.



Echo is trying to succeed where the GlucoWatch did not by improving the technology's ability to permeate a patient's skin, Robert Langer, an institute professor at the Massachusetts Institute of Technology (M.I.T.), wrote in an e-mail to Scientific American. Langer would know—the basic premise of Symphony tCGM is based on ultrasonic transdermal drug delivery technology that Echo licensed from him about a decade ago. Langer's technology focused on administering drugs without needles and even received FDA approval to administer Lidocaine cream, a local anesthetic made by Ferndale Pharmaceuticals, Ltd. With Symphony tCGM, Echo is essentially testing whether this process can safely be reversed to read blood glucose levels.



Glucose monitoring is extremely important to diabetics, to the extent that even somewhat invasive systems—including those that lance a patient's fingertips to draw blood—are used by millions and have sales in the billions, according to Langer. "Everyone I speak to in the diabetes field feels (transdermal monitoring is) very badly needed," he adds.



England cautions, however, that finding an effective transdermal continuous glucose monitoring system is just one step in controlling diabetes. There still is no consensus on what constitutes the "right" glucose level in different patients, he says. Until that is determined, the benefit of having tighter control over blood glucose levels is an "open question," he adds. "We haven't had the technology to study this for any length of time."