Comparison of AID systems (Minimed 670G/770G, t:slim with Control IQ, and DIY Loop)

Hi everyone. As some of you may know, I have recently started Looping. I have wanted to try it forever, but I have to admit I’ve been a bit intimidated and have only recently found the motivation. Thankfully, with the help of an amazing new diabuddy I was able to build my own automated insulin delivery system last weekend. I have really enjoyed learning something totally new in diabetes. I have gone down a rabbit hole of articles, blogs, and social media posts on looping and it has inspired me to write a comparison piece. I have not been paid by any company to write this post. It is meant to be informational and unbiased (mostly). Please remember that this is simply my understanding of how the different systems work. If you have a different understanding, please reach out. I am still and will always be learning!

Minimed 670/770G:

The 670G/770G function in two different modes; manual mode and auto mode. When the user is in manual mode, these systems function similarly to other sensor-augmented pump therapies and use the basal and bolus settings inputted by the user and their clinician. While in auto mode, adjustments are made every 5 minutes by the algorithm based on the sensor glucose value. These are known as “micro-boluses” and replace the pump’s manually programmed basal rate. At this point, the actual configuration of the algorithm is unknown to the public. What we do know is that the algorithm is readjusted every night at midnight and considers the previous 6 days of data. Its adjustments are based on insulin on board (IOB), sensor rate of change, time away from target, and total daily dose (TDD). The Minimed 670G/770G is continuously learning the user. This is beneficial long run, but as it stands, the algorithm cannot account for quick changes in BG averages such as during sick days or during menstruation (because it works from the 6-day average).

t:slim X2 with Control IQ

In Tandem’s hybrid-closed loop model, t:slim X2 with Control IQ, all programmed settings are used when the person’s CGM readings are trending on target, except target and active insulin time (AIT). This is different from the Minimed 670G/770G system where only the carb ratio and AIT are utilized in auto mode. All other settings are determined by the algorithm. The Control IQ algorithm uses temporary basal adjustments to increase/decrease the basal dependent on the sensor glucose prediction. This means that when the user’s sensor glucose is trending on target, the manually programmed basal rates are utilized. Correction boluses can be given hourly (if no other bolus is given w/in hr) by the algorithm and are 60% of the programmed recommended correction. Up to 6 different profiles can be set to help quickly change between different insulin needs (hormones, illness, medication).

DIY Loop

Before I say anything about Loop, I first need to say that it is highly experimental and NOT FDA APPROVED. Loop is a system that can be built using open-source hardware and a software technology called Riley Link to bring together a pump, cgm, and algorithm for automated insulin adjustments. The “do it yourself” hybrid-closed loop system allows the user to control certain settings that are otherwise hard set by commercially available systems, such as SG target. Loop can run in both open-loop and closed-loop variations. In the open-loop variation, the app will make recommendations that must be approved and activated by the user. In the closed-loop variation, those changes are made automatically. The user can easily switch back and forth between the variations. Loop set-up is a bit tedious and takes an experienced techy (or help from one). Compatible CGMs include; Dexcom G6, G5, and G4 with a receiver and Medtronic enlite with a compatible pump. Other CGMs may be usable with help from a third party. Compatible pumps include older Medtronic pumps with certain firmware and Omnipod Eros.

Prediction Timeframes & System-Initiated Settings:

With the two commercial systems, we don’t actually know the basis of all of the automated decisions as they are internal and proprietary.

Minimed 670G/770G

Auto mode uses the PID-IFP algorithm to continuously modify the amount of insulin given by the pump through a “micro-bolus” recalculated by the algorithm every 5 minutes. This micro-bolus is dependent on the user’s sensor readings, and replaces the pump’s basal feature. As previously mentioned, factors influencing these adjustments include; insulin on board (IOB), sensor rate of change, time away from target, and total daily dose (TDD).

t:slim X2 with Control IQ

Control IQ basal and automated corrections are based on the predicted SG value within a 30 minute timeframe. As far as I know, control IQ does not take into account IOB, but is influenced by rate of change and TDD.

DIY Loop

Loop uses temporary basal adjustments based on the user’s active carbohydrates, active insulin, retrospective correction, and glucose rate of change. Each temporary basal is set for 30 minutes, but can be overridden by the algorithm every 5 minutes with an updated sensor glucose reading. The temporary basal rate is determined by the active insulin, the sensor rate of change, the predicted blood glucose, and the eventual blood glucose (at the end of the DIA). The full glucose curve is shown on Loop’s home screen. When closed-loop is turned on, these adjustments will be made automatically, but in open-loop they are merely suggested and need to be activated by the user. From now on, when referring to Loop, I will be referring to closed Loop.

Target Range:

Minimed 670G/770G:

The algorithm targets the sensor glucose to a hard set 120mg/dl. When correction boluses are given, the boluses target a sensor glucose of 150mg/dl and auto basal uses micro-boluses to bring the user down to the targeted 120mg/dl.

t:slim X2 with Control IQ

Control IQ uses the programmed basal settings when the person’s CGM readings are trending between 112.5-160mg/dL. The algorithm then increases/decreases the basal dependent on the predicted sensor glucose within the next 30 minutes. If the glucose is predicted to be above 160mg\dl within 30 minutes, the algorithm will increase the basal. I’m sure there is a max temp basal set by Control IQ, but I am not certain what it is (maybe based on TDD?). If the glucose is predicted to be >180mg/dL within 30 minutes, a correction bolus will be given (60% of programmed). The algorithm will decrease the basal if the sensor glucose is predicted to be <112.5mg\dl and will stop if it is predicted to be <70mg\dl in the next 30 minutes.

DIY Loop

Loop’s correction range, not to be confused with time in range (70-180mg/dl) is the glucose range that Loop uses to take corrective action. It can be set anywhere from a minimum of 60mg/dL to a maximum of 180mg/dL. The sensor glucose will be targeted to an average of the correction range.

User-Initiated Settings:

Minimed 670G/770G

Temp target can be manually activated by the user and targets a sensor glucose of 150mg/dL for an extended period of time, also chosen by the user (up to 12hrs).

t:slim X2 with Control IQ

In exercise mode (manually turned on by the user), the basal rate remains as programmed if the CGM readings are between 140-160mg/dl. Just like in the normal Control IQ setting, an increase in basal will occur if sensor glucose is predicted to be above 160 mg/dl and a correction will be given if predicted to be >180mg/dL within 30 minutes (if a bolus has not already been given within the last hour). Basal insulin will decrease if SG values are predicted to be below 140mg/dL and basal delivery will stop if predicted to be below 80mg/dL within 30 minutes.

In my experience on Control IQ, the simple switch to exercise mode 1-hr before activity was not enough to prevent my lows. To navigate this, I created a basal profile at 50% of my normal basal rate and began setting that profile 1-hr before exercise in addition to turning on my activity mode. This caused me to go into exercise with more elevated BGs resulting in a correction bolus from control IQ (given if predicted to be above 180mg/dl within 30 min). To navigate this issue, I weakened my correction factor on my new exercise profile. It worked out great!

Sleep mode is preset by the user and turns on automatically. Programmed basal rates are used when the patient is trending between 112.5 and 120mg/dl. Basal will be increased if the sensor glucose is predicted to be >120mg/dL within 30 min. Corrections are NOT given in this mode. Basal is decreased when the sensor glucose is predicted to be below 112.5mg/dL and will stop if sensor glucose is predicted to be <70mg/dL within 30 minutes.

Both sleep and activity modes can be left on 24/7 if desired by the user.

DIY Loop

Much of Loop’s algorithm is determined by the user-initiated settings.

Duration of insulin action (DIA) can be set by the user. There are four options for DIA; three of which are exponential models (rapid-acting adult, rapid-acting children, fiasp), and one of which (Walsh) allows the user to set their own DIA (be wary of insulin stacking). The exponential models all have a DIA of 6 hours, but variable peaks.

As previously mentioned, Loop’s target (correction range) can be individualized by each user. For safety, the user must also input a suspend threshold which causes the algorithm to decrease the basal to 0.0 u/hr if the user is predicted to be below that threshold at any point within the set DIA. Additional safety mechanisms include basal and bolus delivery limits, also determined by the user.

Loop has override presets that the user can set to make one single change to insulin requirements. This is done in a percentage and both basal and bolus settings will be adjusted during that override. The user can turn these settings on indefinitely, set them to last for a certain time period, and/or schedule them in advance. Only one override can be utilized at a time.

Boluses:

Minimed 670G/770G:

The user is required to input their carbs into the bolus calculator. Auto mode uses the same carb setting for the bolus calculator in auto mode as it does in manual mode. Correction boluses are calculated by the algorithm using the 1800 rule (1800/TDD) and target the correction to a BG of 150mg/dl. The algorithm then uses the micro-bolus feature to correct the BG to the 120mg/dl target. The user cannot increase or decrease the recommended bolus and extended bolus is not an option in auto mode.

t:slim X2 with Control IQ

Control IQ uses the user's carb factor and correction factor to recommend the bolus. The user can then decide if they would like to increase, decrease, and/or extend the bolus (up to 2 hrs). Of note, if Control IQ predicts that a basal decrease or suspension is required, the extended bolus will NOT be cancelled.

DIY Loop

Though loop uses user-inputted carb ratios and correction ratios, it also allows the user to pick the “food type” consumed to indicate whether the carbs will be quick or slow to digest. Bolus recommendations are therefore based on the predicted blood glucose curve, the user’s suspend threshold, food type, carb ratio, and correction ratio. Loop additionally allows for carb entry into the algorithm even if no bolus is given. This impacts the predicted glucose curve displayed on the Loop home screen.

Impactful programmed settings:

Minimed 670G/770G

Auto mode is impacted by user-set carb ratio and active insulin time. SG target, correction factor, and basal rates are solely determined by the algorithm while in auto mode.

t:slim X2 with Control IQ

All manually programmed settings are used except target and active insulin time.

DIY Loop

All manually programmed settings impact Loop’s algorithm.

Data Accessibility

Minimed 670G/770G

Medtronic’s Carelink is a web based platform that collects information directly from the Minimed 670G/770G through manual upload. With the newer 770G, the user has access to a mobile app that allows them to see their pump and CGM information in real time. This app automatically syncs with carelink every night at midnight preventing the need for manual uploads. The app additionally provides information on bolus events, IOB, and settings.

t:slim X2 with Control IQ

Tandem’s t:connect mobile app allows for a secondary phone display showing the user’s pump and cgm information continuously. The app additionally shows bolus events, IOB, and settings. Like with Minimed, the phone application cannot control the insulin pump. All boluses and changes to insulin settings must be performed on the pump itself.

The t:slim X2’s data can be wirelessly uploaded to the t:connect web based application to be shared with the user’s care team. For non-app users, t:slim X2 with Control IQ can be manually uploaded to t:connect’s web platform or through Tidepool. Both applications are free.

DIY Loop

Loop’s data is available for free through both Tidepool and Nightscout. These accounts must be created and linked. All steps for doing this are online. With the help of my new looping friend, I made a Nightscout account this weekend and have loved seeing my readings live on my computer while working.