How the Medtronic 670G Artificial Pancreas Works: FAQ

On September 28, the FDA announced that it has approved Medtronic Diabetes’ MiniMed 670G system, the world’s first pump/sensor system to be able to dose insulin on its own. Previous systems were able to stop insulin delivery when your blood glucose values dropped too low (or, if you were in the EU, to predictively suspend basal insulin). But the 670G actually uses data from the sensor to give you insulin. This is an enormous step toward a genuine closed loop/artificial pancreas system, and is a really big deal.

Q: But what does it actually do and how does it work?

A: Basically, the goal of the pump/sensor (henceforth known as the 670G system) is to keep you at or close to 120 mg/dl as consistently as possible. Right now your only choices, in terms of target, are 120 mg/dl and 150 mg/dl (in case you want to be really conservative), though Medtronic hopes that future systems might be approved to allow people to set their own targets.

How the Medtronic 670G Artificial Pancreas Works

How it works: You and your healthcare team come up with a set of initial basal rates and you program those into the pump like normal. You also program in your insulin-to-carb ratios as accurately as you possibly can. That’s when things get crazy: instead of programming in your own boluses and corrections, the only thing you tell the pump (other than giving it calibrations for the CGM) is the number of carbs you’re eating at that meal. It gives you a dose of insulin based on your pre-entered insulin-to-carb ratio, and then automatically makes microadjustments and corrections afterwards, with the goal of getting you to 120 mg/dl.

For example, let’s say that you are eating a lunch with 30 grams of carb, and you have a 1:15 insulin-to-carb ratio programmed for that time of day. The only thing you’d enter into the pump would be the 30 grams of carb. It would calculate, based on the ratios you’d previously entered, that you need 2 units of insulin, which it would then automatically deliver. Then it would monitor what happened next. If your blood glucose started to spike, it would give you further microdoses of insulin to bring you back down. If you started to plunge too quickly, it would suspend delivery.

Q: What if I have different insulin-to-carb ratios on different days?

A: It doesn’t really deal with that, though the fact that it can correct for highs will help. Remember that this is the first system of its kind, though, and the engineers are aware of this problem.

Q: Is the system/algorithm “smart”? In other words, does it make refinements to itself based on your blood glucose values over time?

A: The algorithm is “smart” in the sense that, for as long as you’re on the auto mode, it will tweak your basal rates based on your blood glucose readings—which presumably means that its corrections and basal rates would get better over time. (And no, it does not start from zero every time you start a new sensor.) It is not “smart,” however, about insulin-to-carb ratios. Those would be calculated based on the numbers you originally had entered, and would not change over time unless you manually entered those changes.

Q: I like the idea of this closed loop system, but I’m on Dexcom/I’ve had bad experiences with Medtronic sensors in the past. What can you say to reassure me?

A: The new 670G system will also use a new sensor called the Guardian. It’ll look like the Enlite sensor, but its innards will be different. Not only is it approved for 7-day wear, but it’s accurate enough that, well, the FDA trusted it with dosing insulin —which as you know is a deadly medication. (And I’m a Dexcom devotee.) It is not currently available and will roll out with the new 670G system in the spring.

Q: When can I get it?

A: According to Medtronic, the FDA’s approval came even faster than the company itself had hoped, and they’re getting all their manufacturing, training, and reimbursement details in place. They’re hoping to roll out the 670G system in spring of 2017.

Q: But I want it now!

A: Sorry, you can’t get it now. But what you can do is sign up for Medtronic’s Priority Access Pathway Program. This basically means that you get the current 530G system (which has low glucose suspend), and when the 670G is released, you’d be first on the list for the new system, and able to upgrade for $299. Or, perhaps better, there is some way to offer feedback and fill out surveys and get the upgrade for free. For details, check out medtronicdiabetes.com/priorityaccess

Catherine Price

Catherine Price (www.catherine-price.com) was diagnosed with Type 1 diabetes when she was 22 years old. She has written for publications including The Best American Science Catherine Price is a professional journalist who was diagnosed with Type 1 diabetes when she was 22 years old. Her work has been featured in publications including The Best American Science Writing, The New York Times, Popular Science, The Los Angeles Times, The San Francisco Chronicle, The Washington Post Magazine, Salon, Slate, Men’s Journal, Health Magazine, The Oprah Magazine, and Outside, among others. A graduate of Yale and UC Berkeley’s Graduate School of Journalism

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Catherine Price

Catherine Price was diagnosed with Type 1 diabetes when she was 22 years old. She has written for publications including The Best American Science Catherine Price is a professional journalist who was diagnosed with Type 1 diabetes when she was 22 years old. Her work has been featured in publications including The Best American Science Writing, The New York Times, Popular Science, The Los Angeles Times, The San Francisco Chronicle, The Washington Post Magazine, Salon, Slate, Men’s Journal, Health Magazine, The Oprah Magazine, and Outside, among others. A graduate of Yale and UC Berkeley’s Graduate School of Journalism