Review of t:slim (with Control-IQ)

Tandem t:slim X2 Insulin Pump System with optional CGM

How do you choose the best insulin pump for you, or for your child? The key is finding the one with the key features that match YOUR family's needs and lifestyle - while also avoiding your personal deal-breakers. We break it down for you here by presenting a concise summary and clear details (including the pros and cons) of the Tandem t:slim X2™ insulin pump with optional Basal-IQ™ or Control-IQ.™

NOTE: This independent review is provided by Waltzing the Dragon; we are not affiliated with Tandem Diabetes Care. For sales enquiries, please contact the company directly.

Key Features of the t:slim X2™

If you’re looking for an insulin pump system with integrated Continuous Glucose Monitor (CGM), the t:slim X2™ is designed to collaborate with Dexcom CGM (sold separately). What do we mean by “integrated”? The 2 parts – pump and CGM – work together within a single system, with the CGM communicating glucose data to the pump. On a practical level this means that you get all the benefits of CGM, you can see your glucose data on the pump screen (you don't need a separate device to know if you're high, low or in-range), and the bolus function is pre-populated with the current glucose reading, so that you don’t have to manually enter your reading to correct above-target glucose.

You also have the flexibility of using the t:slim as a stand-alone pump (without CGM) if you prefer, or you could choose to wear CGM part-time (like our family does).

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Automatic Insulin Adjustment

But CGM Integration makes possible the BEST feature available in insulin pump systems these days, in my opinion: automatic insulin adjustment. That means that the pump will automatically change the amount of insulin that it delivers based on the sensor glucose readings. This has been revolutionary in taming the diabetes dragon, and Tandem offers two predictive insulin delivery technologies in the t:slim for you to choose: Basal-IQ and Control-IQ.

What is Basal-IQ?

If you’re looking for an insulin pump system that will predict and help prevent lows by shutting off basal insulin delivery when low glucose is predicted, then t:slim's Basal-IQ™ fits the bill. Based on consecutive sensor glucose readings, if the system predicts that glucose levels will drop below 4.4 mmol/L within the next 30 minutes, it will temporarily suspend basal insulin delivery, restarting it automatically when glucose begins to rise. This can go a long way toward avoiding low blood sugar!

What is Control-IQ?

Control-IQ™ takes auto insulin adjustment one step further as a "hybrid closed loop system" which strives to reduce both lows and highs by adjusting basal insulin up or down according to sensor glucose values. So in addition to predicting and preventing low glucose (as Basal-IQ does), Control-IQ technology also predicts and helps prevent high glucose by increasing the amount of insulin the pump delivers. It does all this by predicting your glucose reading 30 minutes ahead and then using 2 ways to maximize your Time in Range:

  • the pump increases basal insulin delivery if your glucose is predicted to rise above 8.9 mmol/L (to head off high glucose) AND decreases basal insulin delivery if your glucose is predicted to fall below 6.25 mmol/L (to prevent a low). The pump stops basal insulin delivery completely if your glucose is predicted to be below 3.9 mmol/L. In addition, Control-IQ also...
  • delivers an automatic correction bolus (once per hour) if your sensor glucose is predicted to rise above 10 mmol/L.   This is the newest tech development in hybrid closed loop systems, and t:slim is the only pump currently available in Canada with this feature.
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From this you can see that Control-IQ uses a target glucose range of 6.25 - 8.9 mmol/L.

You may also be interested to know that the Duration of Insulin Action (DIA) is fixed at 5 hours. This is the time used in the programming development that has lead to both success and safety (and is, arguably, the actual length of time for which insulin continues to act to lower blood sugar), so that's why the DIA setting can't be changed by the pump user.

Control-IQ was approved by Health Canada in November, 2020, for individuals age 6 years and older who weigh a minimum of 25 kg (55 lbs) and have a minimum Total Daily Dose (TDD) of 10 units of insulin. Control-IQ is NOW AVAILABLE to Tandem t:slim users as a software update. 

Speaking of Software Updates...

With the Tandem t:slim X2, a pump update is simply a software update. If new features come out, you don’t need to buy new hardware or wait 4 years to get a new pump; you just connect the pump to your computer using a universal USB, and then download the software update to your existing pump (after meeting the qualification criteria -  for example, watching videos to complete a remote training program).

The trade-off for this updateability (and open USB port that makes it possible) is that the pump is not fully waterproof like most other insulin pumps on the market. The t:slim X2 is water-resistant to 1 meter (3 feet) of water for 30 minutes (watertight IPX7 rating) but it’s recommended that you don’t swim, surf or bathe with it.

Fingerstick BG Checks

If reducing BG checks is a key priority, then note that its integration with Dexcom G6 makes the t:slim X2 the first and only CGM-enabled pump that is approved to let you make treatment decisions without poking your finger. (Also, fingerstick calibrations are not needed for the Dexcom G6.) This can mean virtually an end to fingerstick BG checks.

More details on CGM, including accuracy and the need for fingersticks:

Because of this move away from fingerstick checks to confirm the CGM readings, t:slim is not paired with any particular blood glucose meter or manufacturer, you are free to choose any make and model for your BG meter. The downside of this freedom is that you can only bolus from the pump; t:slim does not offer a meter remote for bolus delivery from an external source. (So we'll have to dig the pump out of our son’s Spibelt for middle-of-the-night blood glucose corrections.)

Design of the t:slim X2

  • Large color touchscreen is intuitively designed and simple to use, eliminating much of the scrolling and button-presses required to operate a non-touchscreen pump.
  • Small size and sleek design. The t:slim X2 is the second smallest insulin pump on the market in Canada (slightly larger than the YpsoPump but much smaller than the Minimed 630G/670G or Omnipod PDM).
  • rechargeable battery is means you don't need to buy replacement batteries anymore. This non-replaceable battery is medical-grade (leaps and bounds above the smartphone battery), lasts up to 7 days (5 days if using CGM) from a fully charged state to a totally discharged state, and has a 4-year minimum service life under normal use conditions.

Recharging can fit into your daily routine, since you do not need to disconnect, and you only need a 5-min daily re-charge. You can plug it in when you sit down for 5 minutes to check email, when you disconnect for a daily shower, or any other time that fits into your usual activities.

Rechargeable batteries are, however, a double-edged sword. Our family used to carry around a lithium battery in our d-kit for emergency backup if the pump battery died unexpectedly. But with t:slim we have to find a plug-in on the fly if we don't stay on top of recharging.

  • The cartridge is designed a little differently than pumps from other manufacturers. It uses pressure to draw the insulin up into the tubing and on to the infusion set (rather than using a piston to push the insulin up). This is both a safety feature and a design choice that allows for smaller, slimmer pump dimensions. As a result, the cartridge fill works a little differently than with other pumps, which may take some getting used to.


  • Tandem employs a full-time psychologist who studies the intersection between diabetes and technology, working with Tandem’s engineers to design a pump that meets makes life with diabetes a little easier. As one example, when glucose is above-target, the Combo Bolus function delivers the glucose correction up front; you don’t have to manually separate it out for a separate bolus and then go back in the combo the food portion of the bolus (like our family had to do with all of my son’s pumps before t:slim). Another example: there’s a “T button” that functions as a one-press Back to Start, for when you want a quick exit from the menus. Also, to make programming of the Personal Profiles easier, you can copy an entire existing time segment and then change certain parts of it; you don’t have to create every new personal profile from scratch. Seemingly small time- and hassle-saving features add up to a big reduction in stress when you’re living with diabetes.

Insulin Delivery Rates & Ratios

Tandem's t:slim X2 has:

  • the smallest basal rate increment of any pump currently available in Canada (though the smallest minimum basal rate belongs to the Medtronic 630G and 670G insulin pumps). This means that you can increase or decrease the basal rate by steps as small as 0.001 units/hr, a step ten times smaller than the pump with the next smallest basal increment. For example, if a basal rate of 1.0 units/hr is not quite strong enough, you could try a basal rate of 1.001 units /hr; with another pump you would have to move up to 1.01 units/hr. This flexibility may be important for small children or anyone who is highly insulin sensitive.
  • the smallest bolus increment at 0.01 units (though the smallest minimum bolus dose belongs to the Medtronic 630G and 670G insulin pumps). This means that if 2.0 units is not quite enough, you can delivery a bolus 1.01U, or 1.02U, or 1.03U, etc. This is less than half the size of the bolus step possible in the pump with the next smallest bolus increment. This is an important feature for small children or anyone who is highly insulin sensitive.
  • the longest duration for a temporary basal function (72 hours = 3 days… we had to re-set our son’s temp basal every 24 hours on his Animas pump) with the largest range (up to 250% of your programmed basal rate).
  • the largest maximum Insulin-to-Carb ratio (I:C) at 1:300, as well as the largest number of time segments (16) in which you can set a different carb ratio across the day.
  • the largest possible Insulin Sensitivity Factor (ISF) at 1:33.3 as well as the largest number of time segments (16) in which you can set a different ISF across the day.
  • You’re no longer limited to switching between Alternate BASAL profiles to match your insulin needs on different days and under different circumstances (workout days, sick days, menstruation, weekend vs weekday, more conservative rates for sleepovers away from home, sedentary travel days spent sitting in a car for family road trips). With the t:slim you can create up to 6 separate Insulin Delivery Profiles to individualize your insulin doses in terms of:
    • Basal Rate (your basal rate in units/ hr)
    • Correction Factor (amount 1 unit of insulin lowers BG)
    • Carb Ratio (grams of carbs covered by 1 unit of insulin)
    • Target BG (your ideal BG level, measured in mmol/L).


The t:slim offers useful alerts to help users follow through on diabetes best practices, including:

  • Incomplete Bolus Alert lets you know if you started a bolus request but did not complete the request within 90 seconds. The alert repeats (with audible tone, or vibration, according to your settings) every 5 mins until acknowledged. (This alone would eliminate MOST of my son’s missed boluses!)
  • High BG Alert that prompts you to give a correction bolus if the CGM says your glucose is above-range AND there is no active insulin remaining (when used with optional Dexcom CGM integration).
  • Low BG Reminder that prompts the user to retest blood glucose after a Low BG has been entered.
  • Missed Meal Bolus Reminder which prompts the user if a bolus has not occurred during the period of time the reminder is set for.
  • After Bolus Reminder prompts the user to check BG at a selected time period (between 1 to 3 hours) after a bolus has been delivered.
  • Low Insulin Alert gives you a heads up if there is 5 units or less of insulin remaining in the cartridge.

Other Considerations

  • If you happen to experience a pump failure, same-day replacement is available in and around major centres.
  • If you like “in house” d-supplies, you should know that Tandem makes and manufactures their own cartridges.

We hope the above information helps you to choose an insulin pump, for yourself or for your child, that best fits your unique needs and preferences... all the best with your pump shopping!