Closed-Loop Control Algorithms (Artificial Pancreas)

Closed-Loop Control Algorithms (Artificial Pancreas)

A closed-loop control algorithm is the software inside an "artificial pancreas." It takes glucose readings from a continuous glucose monitor (CGM) and tells an insulin pump how much to deliver, adjusting in real time [1]. Test strips haven't left the picture, though. Below we explain how the main algorithm types differ and what each US system does when the sensor goes quiet, which is exactly when a fingerstick meter matters most.

Three ways to decide on a dose

Researchers have built three main families of control algorithm [1]. A proportional-integral-derivative (PID) controller reacts to glucose in three ways at once: how far it is from target, how long it has been off target, and how fast it is changing [1]. A model predictive control (MPC) algorithm runs a model of the body forward in time, then picks the insulin delivery that keeps predicted glucose closest to target over a set window [1]. Fuzzy logic, the third family, follows approximate rules meant to capture how experienced diabetes clinicians reason [1].

The systems sold in the US don't all use the same family. A 2021 review classed the MiniMed 780G's algorithm as "PID with insulin feedback" [1]. Tandem's Control-IQ+ works from forecasts: when it predicts that sensor glucose will be at or below its target range 30 minutes from now, it starts cutting insulin [2]. In clearing Control-IQ+, FDA noted that its algorithm design is unchanged from the earlier Control-IQ [2]. Insulet's SmartAdjust algorithm, which runs the Omnipod 5, also adjusts delivery on current and predicted glucose [3].

Some algorithms also learn from the person wearing them. The Omnipod 5 works out an adaptive basal rate for each Pod [4]. The iLet Bionic Pancreas goes further. It starts from body weight and sets basal and correction doses on its own [5]. For meals, the user only estimates the meal's size relative to their usual breakfast, lunch or dinner, and the software sizes the dose [5]. Our CGM hub goes deeper into the control math in PID vs. MPC Algorithms in Automated Insulin Delivery.

When the sensor goes quiet

Here's what surprised us: the four systems below each handle a CGM gap differently, and only the iLet is built to keep dosing from fingerstick readings [5]. The details come from each system's FDA record or user guide, as of October 2026.

Tandem Control-IQ+

Control-IQ+ keeps adjusting basal insulin and correction boluses for the first 20 minutes that the CGM and pump are out of range [6]. After 20 minutes without a CGM reading, it reverts to the programmed basal rate. Tandem's guide gives examples of when that happens: the pump and CGM drift out of range, a sensor is starting up, a sensor session ends, or there's a transmitter or sensor error [6].

Omnipod 5

After 20 minutes without sensor values, the Omnipod 5 moves into a state Insulet calls "Automated: Limited" [4]. It then delivers whichever is lower, the Manual Mode basal rate for that time of day or the Pod's adaptive rate, and it stops adjusting for current or predicted glucose [4]. After an hour of missing sensor values, the app raises an advisory alarm [4].

MiniMed 780G

When the 780G decides sensor data aren't good enough for automatic dosing, it switches to Safe Basal, a patient-specific rate, for no longer than 90 minutes [7]. If the problem clears within that window, automatic adjustment resumes. If it doesn't, the pump drops to Manual Mode, where the labeling says therapy adjustments should rest on blood glucose meter readings rather than sensor values [7].

iLet Bionic Pancreas

The iLet has a feature FDA calls "BG-Run mode." The user enters meter readings by hand, and the software keeps dosing from them for a limited time [5]. FDA describes the feature as temporary, for the shortest time possible, and says that if the CGM stays offline for an extended period, a countdown appears and dosing stops [5]. In a 54-person study of the feature, participants spent a median of 49.5 hours in BG-Run mode and entered a median of 9 fingerstick readings in the first 24 hours [5]. The labeling says not to use the iLet if you're unable or unwilling to test with a meter when CGM input isn't available [5].

Where a meter reading still enters the loop

Strips show up in the labeling even when the sensor is working. FDA lists an Accu-Chek Guide Link meter and Accu-Chek Guide test strips as parts of the MiniMed 780G system [7]. With the Guardian 4 or Simplera Sync sensor, calibration isn't required, yet the system uses every meter reading, whether typed in or sent from the linked meter, to calibrate the sensor [7]. On a 780G, then, a fingerstick is more than a spot check. It feeds into the sensor's calibration.

Other systems treat the meter as a backup input. The Omnipod 5 SmartBolus Calculator can take a fingerstick reading in place of a sensor value [8], and Insulet's guide says to check with a meter when sensor values don't match symptoms [4]. On the t:slim X2, CGM values fill the bolus calculator's glucose field automatically while Control-IQ+ is on [2]. The Dexcom G7 is cleared to replace fingerstick testing for treatment decisions and is factory calibrated, with optional fingerstick calibration [9]. Its labeling still says to use a meter when readings don't match how you feel [9].

One sensor paired with an AID system still runs on scheduled fingersticks. The twiist AID System works with the implanted Eversense 365 [10]. That sensor's FDA clearance calls for four fingerstick calibrations during an initialization phase, then one every 24 hours through day 13, then one a week from day 14 [11]. Of the sensors in this article, it's the only one that builds strip use into every week of wear.

What this means for your strip supply

Closed loops cut routine fingersticks, but none of them retires the meter. The ADA's Standards of Care in Diabetes—2026 say people using CGM must also have access to blood glucose monitoring, for example when the CGM seems inaccurate, during warm-up, when transmission is disrupted, or for calibration [12]. The 780G labeling goes a step further: it says pump therapy isn't recommended for people unwilling or unable to do meter readings [7]. How many strips to keep on hand, and when to trust a fingerstick over the sensor, are decisions to make with your care team.