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Apple Health FAQs

How does Loop use Apple HealthKit?

Loop uses Apple HealthKit as long term storage for glucose, insulin and carbohydrates. But there is more going on than simple storage.

It is important that permissions for Loop be properly configured for the Health app.

To view the list of data stored in Health

  • Tap on the Health ❤ icon to open the app
  • Tap on Blood Glucose, Carbohydrates or Insulin
  • Scroll all the way to the bottom
  • Tap on Show All Data

To Set Blood Glucose, Carbohydrates and Insulin as Favorites

  • Tap on the Health ❤ icon to open the app
  • There's a toolbar at the bottom of the screen (always visible in the app)
  • Tap on the Browse icon (bottom right of toolbar)
  • Tap on
    • Other Data for Blood Glucose and Insulin
    • Nutrition for Carbohydrates
  • Tap each item, scroll down to Options section and tap on Add to Favorite
  • Repeat until all three are added
  • Tap on the Summary (bottom left icon of toolbar); Favorites show up first

HealthKit Plots

The health app on the Loop phone provides useful plots of data since you started to Loop with that Apple ID. Examples for insulin delivery and carbohydrates are shown in the graphic below. New versions of iOS modified details of the display with the same or improved capabilities.

example insulin and carb plots visible with HealthKit

HealthKit Details

Glucose and Apple HealthKit

For Dexcom users with the Dexcom app on the Loop phone, the Dexcom app writes the value to Health with a 3-hour delay.

Loop reads the Dexcom information at the same time the Dexcom app gets the reading from the transmitter. It uses the glucose value to update predictions and stores it in Health.

If you look at your Health glucose readings, you'll notice the Loop icon for the last 3 hours and the Dexcom icon for times earlier than that.

All other CGM readings are reported with the Loop icon and there is no transition after 3 hours.

You may also notice that the Dexcom numbers get smoothed out. For example, the Dexcom readings, when they first are read from the transmitter may bounce up and down a bit. The Dexcom app will retrospectively smooth the numbers, changing what is displayed in their app compared to the original reading. The last 3 hours of data from Loop does not show that smoothing - it reports the value sent by the transmitter. If you suspect a sensor is not behaving well, check the Loop glucose plots compared to the Dexcom plots to assist in your evaluation. It might be time to confirm glucose with a fingerstick meter as well.

Carbohydrates and Apple HealthKit

In Loop 2.2.x, if you set Apple Health app permissions to allow it, Loop will read carbohydrates from the Health app. If you give a third-party app permission to store carbohydrate data in Health, and do not realize that Loop reads that information, you might get unexpected insulin delivery based off those carbs. To avoid that unanticipated behavior, the directions tell you to set permissions to allow Loop to write to carbohydrate storage but not read.

In Loop 3, the option to read from Health carbohydrates is explicitly disabled and can only be enabled by setting up special parameters when you build the app. The insructions for the code customization are not in LoopDocs yet. If it is important to you to use a third-party app to record carbohydrates and have Loop read the information and automatically dose with insulin, ask for help in zulipchat.

Insulin and Apple HealthKit

The relationship between Loop and Apple HealthKit is very important to understand if you ever need to do one of these actions:

  • Dose insulin from another source (injection, smart pen)
  • Remove insulin that wasn't really given (failed site or forgot to reattach a tubed pump)

Be Cautious

Allowing users to delete events is fairly risky. If a user deletes a dose accidentally, or does not understand the IOB impact while in Closed Loop, then Loop may start giving insulin that is not needed.

One method to deal with insulin that wasn't given is to go Open Loop for 3 to 6 hours. However, if you take care, you can remove insulin from Loop.

Developer Notes: Pump Events and Insulin Delivery

Loop stores Pump Events separately from Insulin Delivery. With permissions set to allow Loop to read insulin from Health (recommended), the Insulin Delivery store contains doses entered from Health as well as the subset of pump events that represent doses.

Pump Events are displayed by tapping an insulin chart on the main screen and viewing the Event History tab.

When you delete a pump event using the Event History interface in Loop, the associated entry in Insulin Delivery is not deleted.


  • When Loop commands the pump to provide a bolus, either manual or automatic, it is shown in the Loop Event History and in the Health app insulin data list
    • It may take a Loop Cycle or two to show up in Health, but it will appear
  • When you add insulin, such as from an injection, to the Health app, Loop reads it and adds it to IOB
    • It will not be added to the Event History because this is not a pump event
    • Loop 3 adds a new feature that allows you to add non-pump insulin from within the app instead of requiring you to add it inside the Health app
  • If you delete an entry from the Loop Event History list, but leave that same entry in Health, Loop reads it back from Health
    • It will not show up in the Event History, but it will still contribute to IOB
    • You must delete a pump event from both Loop Event History and Health data; it is best if you do this within one Loop Cycle
    • If that dose showed up in Event History but you could not find it in Health, look again after the next Loop cycle
  • If you delete an entry from Health, but leave that same entry in Loop Event History, Loop reports it to Health again
    • You must delete a pump event from both the Loop Event History list and Health data; it is best if you do this within one Loop Cycle

Pro Tip

Write on a piece of paper the times and values you think you should delete.

Look at those values in both Loop Event History and Health Insulin data list.

Record what Loop is reporting as IOB.

Review the values one more time, and then delete those entries in both places. Review IOB again. If you made a mistake, you can refer to that written list and adjust appropriately.


Loop keeps track of how much basal is delivered so the IOB is properly reported. In older versions of Loop, there may be occasional display glitches, but the internal accounting is correct and updates every Loop Cycle.

Developer Notes: Scheduled Basal is Not a Pump Event

Scheduled basal is not a pump event so you will not see it listed in the Event History tab.

Scheduled basal does not affect IOB when delivered as scheduled.

The Insulin Delivery store keeps track of the insulin delivered via scheduled basal.

Loop updates the amount of insulin delivered through basal (both scheduled and temporary) to Health at regular intervals - this does not happen every Loop Cycle when basal rates are not changing. The updates to Health happen:

  • At midnight
  • When the scheduled basal rate changes
  • When a temporary basal rate changes

A simple example to illustrate this - for a pump with smallest insulin delivery of 0.05 U:

Temp Basal (TB)
12:00 AM
0.4 U/hr
--- --- Start of Day / Start of Example
06:00 AM
0.5 U/hr
--- 06:00 AM
2.4 U
Loop reports insulin delivered by basal for the last 6 hours when the scheduled basal rate has a new entry
--- 07:15 AM
0.0 U/hr
07:15 AM
0.6 U
Loop reports insulin delivered by basal since last report up to time TB starts
--- 07:45 AM
TB expires
07:45 AM
0 U
No insulin was delivered during TB
08:00 AM
0.4 U/hr
--- 08:00 AM
0.1 U
Loop reports insulin delivered by basal since last report; the scheduled basal rate has a new entry

Tidepool and Apple HealthKit

If you have a Tidepool account and use the Tidepool uploader on your Loop phone, the data in Health is uploaded to your Tidepool database where you can view displays with the Tidepool web browser tool.

How Do I Modify Apple HealthKit Permissions

You can review the Apple HealthKit permissions screen at any time.

Simply open the Apple Health app (❤ icon)

  • Find the toolbar at the bottom that says Sharing
  • Scroll to the bottom of Sharing
  • Select Apps
  • Select Loop

At this point, you can review and modify the settings.

How Do I Change Glucose Units?

The glucose units (mg/dL or mmol/L) Loop uses match what is in Apple Health. Once you connect a device that reports glucose to the phone, make sure the units match the device. Note - you can change units for Dexcom Share and it translates units for you - not sure about other devices.

  • These instructions to change Blood Glucose units are for iOS 15
    • Select the Health app (Heart icon)
    • There's a toolbar at the bottom - select Browse
    • Scroll to find Vitals
    • Select Blood Glucose
    • Scroll to the bottom and select Unit
    • Tap on Unit, if it isn't right, and select the correct units
    • While you are there - go on and select Blood Glucose as a Favorite - it will be easier to find next time