Continuous Glucose Monitoring: Navigator Beats Rival Devices

January 14, 2013

A small but unique 3-way comparison of continuous glucose-monitoring (CGM) devices for patients with diabetes has revealed marked differences in performance between the products. However, the device that did best in the study is no longer on the market in the United States, the researchers observe.

Edward R. Damiano, PhD, associate professor of biomedical engineering, from Boston University, Massachusetts, and colleagues report their findings in Diabetes Care. Senior author Steven J. Russell, MD, PhD, from Massachusetts General Hospital, Boston, explained to Medscape Medical News that the Navigator CGM device (Abbott Diabetes Care) outperformed the other 2 products, the Seven Plus (DexCom) and the Guardian (Medtronic), but unfortunately, for commercial reasons, the Navigator is no longer available in the United States. However, it is on the market in Europe and some other countries, such as Israel and Australia, he noted.

Dr. Russell said the findings of the study are still relevant, however. "The Medtronic device is still available in the US, with the largest market share, but it had the worst performance of the 3 sensors that we tested. Also, a lot of people are still using the DexCom Seven Plus." He added: "We've always hoped that there might be some hue and cry for them to bring the Navigator back to the US market, especially when we are publishing data showing that theirs was the best sensor."

If you look at it from the user's point of view, you have to think about things like usability, and here Medtronic has the advantage.…The DexCom device is also very user-friendly, but the Navigator user-friendliness is very low.

Asked to comment on the findings, Roman Hovorka, PhD, from the University of Cambridge Metabolic Research Laboratories, in the United Kingdom, who was not involved with this study but has published similar assessments of CGM devices, said the results of Damiano et al are "robust."

However, he pointed out that accuracy of sensors in the CGM devices is "just one of the factors" that determine usage. "If you look at it from the user's point of view, you have to think about things like usability, and here Medtronic has the advantage and they also have brilliant customer service. The DexCom device is also very user-friendly but the Navigator user-friendliness is very low, to be honest, and I wouldn't say the Navigator is overall the best system. It's a complicated mixture of factors."

CGM Can Improve Glycemic Control According to Published Data

Dr. Russell explained that real-time continuous monitoring of glucose — as opposed to a glucose finger-prick test — is a relatively new method of following glucose levels among patients with diabetes, with less than 20% of people in the United States currently employing it, although it is generally covered by insurance plans. It can be used by those with type 1 diabetes or people who have type 2 diabetics who are insulin-dependent, he said.

Dr. Hovorka says use of CGM devices is much lower in Europe, primarily due to reimbursement issues, but adoption "is increasing."

The first generation of CGM devices were not that good "and people became discouraged, because they were not very accurate or reliable," Dr. Russell noted. But the third- and fourth-generation devices now in use "are much more consumer friendly," he said, and "they provide tremendously more information for people to manage their own diabetes."

The devices consist of a small sensor around 1/2 cm long, inserted just below the skin — "in essence, a glucometer strip turned inside out and put under the skin" — that is connected to a transmitter about the size of a quarter. The latter transmits the signal to a receiver, "which kind of looks like an iPod," he remarked.

People can look down at any time and see an estimation of their blood glucose and they can set the device to give an alarm if the glucose is dropping too low, or running too high.

CGM measures glucose in the interstitial fluid, which is then calibrated with blood glucose measurements intermittently and allows an estimation of glucose levels every 5 minutes, 24 hours a day. "People can look down at any time and see an estimation of their blood glucose, and they can set the device to give an alarm if the glucose is dropping too low or running too high and respond quickly to that. And you get to see the trend of blood glucose, which is really quite important," Dr. Russell explained.

Dr. Hovorka noted that the Medtronic system differs slightly from the others, in that the CGM signal is sent to its Veo insulin pump, which is programmed to deliver a basal rate of insulin continuously, with delivery being boosted if necessary or shut off entirely if glucose falls too low — for example, while the wearer is sleeping.

Dr. Russell said published data have shown that people who use CGM devices can improve their glycemic control, both by reducing their mean blood glucose and also by reducing hypoglycemia.

He added that the field is very fast-moving, and even newer versions of some of these devices are already available. DexCom has a new G4 platinum CGM device, which has been approved by the US Food and Drug Administration and is available in the European Union, and Medtronic has a newer version of its device — with a novel sensor called Enlite, "which is much more comfortable," Dr. Russell said, and is again used together with the Veo insulin pump and is available in Europe.

To this end, his team has just completed a new 3-way comparison of the Navigator device with the DexCom G4 platinum device and the newer Medtronic product in 24 patients, for which they have submitted an abstract to the American Diabetes 73rd Scientific Sessions this year. "Our preliminary analysis suggests that the new DexCom device is as good as, or even better than, the Navigator," he said.

Navigator Better on Accuracy, Precision, and Reliability

Although previous research has compared different CGM devices, the methodology of the current published study is unique, Dr. Russell stressed to Medscape Medical News. "Ours was the first study to rigorously compare the performance of these devices across a wide blood glucose range, in a realistic setting. It's a head-to-head-to-head — in other words, on the same person at the same time under everyday conditions where the blood glucose is changing rapidly, and it varies all the way from very low blood glucose to very high blood glucose."

He and his colleagues compared the 3 CGM devices in 6 patients with type 1 diabetes (average age, 52 years, with mean diabetes duration of 32 years) who each participated in two 51-hour closed-loop blood glucose control experiments in the hospital. Venous plasma glucose (PG) measurements were obtained every 15 minutes and were paired in time with corresponding CGM glucose (CGMG) figures obtained from the 3 devices: the Navigator, the Seven Plus and the Guardian, worn simultaneously by each subject. Errors in paired PG-CGMG measurements and data-reporting percentages were obtained for each device.

"The Navigator had the best overall accuracy, with an aggregate mean absolute relative difference [MARD] of all paired points of 11.8, and an average MARD across all 12 experiments of 11.8," Dr. Damiano and colleagues report. "The Seven Plus and Guardian produced aggregate MARDs of all paired points of 16.5 and 20.3, respectively, and average MARDs across all 12 experiments of 16.5 and 20.2, respectively." Data-reporting percentages, a measure of reliability, were 76% for the Seven Plus and nearly 100% for the Navigator and Guardian.

"A comprehensive head-to-head-to-head comparison of 3 CGM devices for blood glucose values from 36 to 563 mg/dL revealed marked differences in performance characteristics that include accuracy, precision, and reliability. The Navigator outperformed the other 2 in these areas," they conclude.

CGM Will Really Take Off With Advent of Artificial Pancreas

To Medscape Medical News, Dr. Russell said, "Even though we had a relatively small number of subjects, the number of unique observations was quite high. There seemed to be as much variation between 2 different sensors within a subject in terms of accuracy as there was between 2 different subjects. This suggests that the accuracy depends on variation in the sensor-to-sensor manufacture and not on difference in the biology of the volunteers."

He noted that CGM will really come into its own when the so-called "bionic" — or artificial — pancreas becomes a clinical reality. He and his colleagues are working on a bihormonal one that utilizes both insulin and glucagon, and many other academic and commercial groups in the United States, Canada, and Europe are researching similar products, most of which employ insulin only, including teams from Medtronic and Animas, a Johnson & Johnson subsidiary.

Dr. Damiano and colleagues have disclosed no relevant financial relationships. Dr. Horvorka has received research support from Abbott, DexCom, and Medtronic.

Diabetes Care. Published online January 3, 2013. Abstract