Dexcom Time Representations

Owned by Toni Connelly
Nov 12, 2024
2 min read

Inform receives two representations of time from Dexcom and both are reported for each glucose value. The top-level of the CGM record also includes start_time and end_time fields that define the UTC day that the CGM record represents.

What We Receive from the CGM Source:

  1. system time - the time according to the system clock at which observation was made.

    1. Always in UTC.

    2. Inform Field time

  2. display time - the time displayed on the receiving device when the observation was made.

    1. This is in user local time if the receiver has a concept of local time (e.g., the CGM mobile app) OR

    2. It is in UTC time if the CGM receiver does not have knowledge of the user’s local time (e.g., Dexcom handheld receiver).

    3. Inform Field display_time

What We Use from the Validic User Profile:

  1. utc_offset - For Dexcom, this information is always requested from the patient if it has not previously been stored.

    1. It’s determined based on the location stored in the Validic user profile.

    2. Clients may set the location during user provisioning or any time after the user has been provisioned.

    3. Clients may update the location at any time to account for timezone changes.

    4. The user is asked to provide their home timezone when connecting to the CGM source via the Validic Marketplace if a location is not already set in their Validic user profile. If they had previously provided this timezone information, they will not be prompted for it again.

    5. The offset_origin for CGM sources will always be "user_defined".

Branching Logic Recommendation for CGM Time:

IF display_time does not match time, then the display_time is directly from the source and can be considered a trustworthy indication of user local time.

 

IF display_time matches time, then it is possible that either of the following two scenarios applies:

  1. The user is actually located in GMT timezone (+00:00)

  2. The receiver has no concept of user local time and is reporting UTC time for the display_time

There’s no clear way to differentiate between these two scenarios based on the data we receive from the CGM sources. Therefore, timezone adjustment may be needed to the display_time based on the user timezone the client determines is most appropriate.

To handle this, clients can choose the best option(s) for their needs including:

  • use the user local timezone recorded by their own platform/app

  • ask the user to confirm their local timezone and use that

  • use the utc_offset in the CGM record, which is based on the information stored in the Validic user profile