Type 1 diabetes

Hybrid closed loop: 70% threshold of use defined to meet glycaemia targets

Real world experience of hybrid closed loop (HCL) has suggested people need to be using the system 70% of the time in order to achieve their 70% time in range (TIR) glycaemic targets.

The US study of 276 children and adults with type 1 diabetes prescribed the 670G HCL system – a 670G insulin pump, Guardian sensor 3 CGM, and a control algorithm that calculates basal insulin delivery every 5 minutes aiming for a target glucose of 120 mg/dL.

The study found a higher percentage use of HCL in adults 26-49 years (79%) and older adults ≥60 years (85%), which remained stable over a year, compared to youth <18 years (71%) and young adults 18-25 years (71%) in whom HCL use also declined over 12 months.

Consequently, TIR was higher in adults (71%) and older adults (74%) compared with youth (61%) and young adults (63%).

“HCL use of 70.6% predicted TIR of 70% or higher with a sensitivity of 85.1% and a specificity of 58.3% and area under the curve of 0.77,” the study said.

“Age at HCL start, BG checks per day and CGM use were variables significantly associated with 70.6% HCL use.”

Overall, 20% of participants discontinued HCL in the first year of use – mostly youth or young adults (66%) versus adults and older adults (33%) – and 9% used it only intermittently.

Reasons previously described for discontinuation of HCL use in youth and young adults include difficulties with CGM sensor calibration and persistent alarms.

The study, published in Diabetes, Obesity and Metabolism, said that 70% HCL use may be a useful clinical goal for clinicians when helping people with diabetes struggling to sustain HCL use and not meeting TIR of 70% or higher.

“While clinicians should encourage as much HCL use as possible, the identified threshold of 70% HCL use indicates that perfection is not necessary to realise glycaemic targets with HCL,” it said.

“CGM use of 80% or greater and checking BG four or more times per day were self-management behaviours that increased the odds of HCL success in this study, suggesting these are important self-management goals to improve 670G HCL success.”

Professor David O’Neal

Commenting on the study, Professor David O’Neal told the limbic that the findings were very relevant to clinical practice and implementation of new technologies in Australia..

“The same hurdles that are faced by our colleagues in North America, are faced by us. Certainly it goes to show two things. First, it’s just not a matter of handing out devices but we do need to have the structures in place to support these devices and support the people living with diabetes who are using these devices.”

“And secondly, youth or younger adults didn’t do as well as the older people and it suggests that perhaps they do need more resourcing in place to ensure that the technology is used to its best potential.”

Professor O’Neal said that the 670G was a first generation system and while it made a very big difference to glucose control in people who were able to use it to its potential, it was fairly demanding on the user as well.

“For example, people still need to bolus for meals and assess carbohydrate content of the meals. They need to calibrate the device. And they usually need about 3-4 glucose checks each day and if they don’t put in this information or there is a discrepancy through the sensor, they get kicked out of closed loop.”

“The second generation systems are coming out – like the 780G – and the new closed loop systems I suspect will be much more user friendly. They will be factory calibrated, they won’t require a fingerprick calibration and therefore that interface… will be much more user friendly.”

Professor O’Neal, from St Vincent’s Hospital Melbourne and the University of Melbourne, said people with diabetes will want to choose the combination of technology that best suits their individual needs and preferences.

“We do know that the more you use the device, the better your outcomes. To get to that 70% time in target, you need to use the device for about 70% of the time.”


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