Month: October 2018

Sync’ing blood glucose data over Bluetooth to HealthKit

The code for this project is on my GitHub (here).

While newer blood glucose monitors (BGM) have Bluetooth capability (BLE), they are often designed only to sync data to their own clouds. Many applications call for mixing glucose measurements with data like weight, activity, carb consumption from other apps to enable consumers themselves, coaching, or care teams to use the information directly.

This code pulls glucose measurements from a BLE-enabled BGM and stores in:

  • HealthKit. Many apps and EHRs have HealthKit integration and can use HK as a channel to import glucose data.
  • Open format. Developer can integrate into other database systems.
HealthKit result

The code was developed using a Contour Next One BGM since it was found in a study published by the Diabetes Technology Society to be the most accurate of the set of 18 BGMs tested and one of the few to meet the FDA accuracy standard for glucometers.

The Bluetooth Forum developed a standard “GATT” profile for BGMs. Details can be found here.

Reads from the BGM are performed via its “Record Access Control Point (RACP)” characteristic. The code writes to RACP requesting data from the Bluetooth Glucose Measurement and Glucose read more

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Blood Glucose Meter tear down: Contour Next One

A recent study by the Diabetes Technology on a cohort of 1000 people found that of 18 popular glucometers in the US, only 6 met the FDA standard for accuracy:

Investigation of the Accuracy of 18 Marketed Blood Glucose Monitors. David C. Klonoff, Joan Lee Parkes, Boris P. Kovatchev, David Kerr, Wendy C. Bevier, Ronald L. Brazg, Mark Christiansen, Timothy S. Bailey, James H. Nichols and Michael A. Kohn. Diabetes Care 2018 Aug; 41(8): 1681-1688.

and another good study on accuracy here: Performance Evaluation of Three Blood Glucose Monitoring Systems Using ISO 15197

I was surprised by 2 things:

  1. Of course that only 6 BGMs met the standard….
  2. The FDA standard itself which specifies accuracy of only +- 15mg/dL at or below 100mg/dl and +-15% above that number. If your fasting blood glucose was measured at say 95mg/dl, that could mean to a 95% confidence level you are anywhere from 80mg/dl (relatively close to hypoglycemia) to 110mg/dl (pre-diabetic).

I decided to take a look inside the best scoring BGM: Contour Next One. Basically it looks like this:

PCB top side

Top side features a simple connector housing for the strip insert, a Toshiba custom analogue front end and an MCU.

A decap of the MCU reveals that it is from Renesas and is likely a R5F51135ADLJ (128KB ROM flash, 32KB RAM, 8KB data flash). This is based on Renesas’ proprietary RX CPU architecture read more

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