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New Fluorescent Technology for Glucose Sensors are Accurate

Posted: Wednesday, June 17, 2009

A novel continuous glucose monitor that uses fluorescence to provide a read-out of blood sugar appears to be accurate, especially in the hypoglycemic range, researchers said at ADA.

In a small trial of five patients, values displayed by the new device were comparable to those determined by laboratory blood glucose samples, William H. Markle, president of device manufacturer GluMetrics of Irvine, Calif., said at a poster session at the American Diabetes Association meeting.

"What's unique about it is that it's a nonenzymatic sensor, so it's not consuming glucose in the process of sensing," Markle said. Ostensibly, that's beneficial for patients entering a bout of hypoglycemia. In fact, the device was most accurate in the lower ranges of blood glucose. "Unlike enzymatic sensors, the lower [blood glucose] goes, the more accurate it is," Markle said.

Having a device with good accuracy in the hypoglycemic range is critical, Howard Wolpert, M.D., of Harvard, said in an interview. "This study indicates that fluorescent technology has real sensitivity in low glucose ranges, so I think there's real promise there," Dr. Wolpert said.

He explained that this issue is particularly relevant because of recent findings that hypoglycemia is associated with markedly increased mortality, especially in intensive care unit patients.

The sensor is based on quenched fluorescence using a modified boronic-acid glucose receptor, the researchers said. A blue-light challenge reveals a green fluorescent response, and the higher the level of glucose, the higher the fluorescence.

To test their device, the researchers recruited five volunteers with Type 1 diabetes for an eight-hour, outpatient feasibility study. The sensors were inserted in a peripheral vein at the antecubital fossa with a 22 Ga needle and a retractable cannula. One failed upon insertion because of mechanical damage, Markle said.

Readings from the other four sensors were taken at one-minute intervals and compared with hospital and lab blood glucose measurements from venous samples in the contralateral arm once every 15 minutes.

The researchers found that 100% of all values below 75 m/dL were within about 15 mg/dL of the reference values, and 94.5% of all values of at least 75 mg/dL were within plus or minus 20 mg/dL of the reference values. The mean absolute relative difference was 8.95%, Markle said, and no adverse events were reported.

Vivian Fonseca, M.D., of Tulane University and the Scott and White Clinic at Texas A&M University, said one of the most important aspects of the novel device is its intravascular location, which gives it access to the actual bloodstream, as opposed to tissues below the skin. "Conventional glucose monitoring measures glucose in interstitial fluid in subcutaneous tissue, which is problematic as there is a lag between the two," Dr. Fonseca said. Instead, he said, this device measures blood glucose in "real-time." "There is a great need for a device like this, which may revolutionize how we take care of patients with diabetes in the hospital," he said.

Noting that many previous efforts have failed, he called this study "very small and, at best, preliminary." "Most importantly, they have not tested it in patients in the hospital with critical illness. I suppose that will be the next step," Dr. Fonseca said.
Markle said that since this was the "very first human experiment" with the device, more studies will need to be done.