What should I do if my sensor reading and blood glucose value don’t match?
DEXCOM ONE+ CONTINUOUS GLUCOSE MONITORING SYSTEM READING AND METER VALUE
Whether you’re new to Dexcom or experienced, review product instructions before using the Dexcom ONE+. Keep using your BG meter to make treatment decisions until you know how Dexcom works for you. Your meter gives you one number, if you test twice (using the same or a different meter) it gives you another number, and your Dexcom ONE+ gives you a third. What do you do with all those numbers?
The test
The blood glucose test your doctor does is considered a more accurate glucose number than any products you use at home. Both meters and Dexcom ONE+ are compared to that doctor’s test to measure accuracy in clinical studies. They are not compared to each other. Additionally, keep in mind that CGM systems measure the interstitial glucose that deviates slightly from the current blood glucose due to physiological reasons. Because of this, the Dexcom ONE+ reading and meter value are unlikely to be exactly the same number, but they should be close. A difference between blood glucose readings and Dexcom CGM readings of up 1.1 mmol/L for readings lower than 3.9 mmol/L and up to 20% for readings higher than 3.9 mmol/l is within the medically acceptable range that is the industry standard. Remember that the lag time is the largest under extreme conditions such as exercise. The trend arrow provides a useful tool to estimate where the readings are heading and how fast. In sensors with optional calibration we recommend to consider a calibration when differences are between 20 – 30% and when above 30% to call for action and use BGM for treatment decisions.
The blood glucose test your doctor does is considered a more accurate glucose number than any products you use at home. Both meters and Dexcom ONE+ are compared to that doctor’s test to measure accuracy in clinical studies. They are not compared to each other. Additionally, keep in mind that CGM systems measure the interstitial glucose that deviates slightly from the current blood glucose due to physiological reasons. Because of this, the Dexcom ONE+ reading and meter value are unlikely to be exactly the same number, but they should be close. A difference between blood glucose readings and Dexcom CGM readings of up 1.1 mmol/L for readings lower than 3.9 mmol/L and up to 20% for readings higher than 3.9 mmol/l is within the medically acceptable range that is the industry standard. Remember that the lag time is the largest under extreme conditions such as exercise. The trend arrow provides a useful tool to estimate where the readings are heading and how fast. In sensors with optional calibration we recommend to consider a calibration when differences are between 20 – 30% and when above 30% to call for action and use BGM for treatment decisions.
The rule
To use the 30/30% rule follow these steps using the table below:
To use the 30/30% rule follow these steps using the table below:
- In the first column, find the BG meter value closest to yours.
- In that row, check whether your CGM reading fits into the range in the second column.
- If it fits, treat using the number that best fits your symptoms, whether it’s from your Dexcom ONE+ or your BG meter.
- If it doesn’t fit, don’t treat with your Dexcom ONE+. Use your BG meter value instead.
For example, if your BG meter value is 8.0 mmol/L (shown in orange in the following table) and your CGM reading is:
- 6.0 mmol/L, treat using either your Dexcom ONE+ or your BG meter
- 5.0 mmol/L, optionally calibrate Dexcom ONE+, treat using your BG meter and submit a Product Support Request to report to Dexcom if the issue persists.
This table provides CGM readings that are within ± 30% of the BG meter value for BG meter values ≥3.9 mmol/L and within ± 1.67 mmol/L of the BG meter value for BG meter values <3.9 mmol/L.
BG Meter Value (mmol/L) | Sensor Reading (mmol/L) | BG Meter Value (mmol/L) | Sensor Reading (mmol/L) | BG Meter Value (mmol/L) | Sensor Reading (mmol/L) |
2.2 | LOW-3.87 | 9 | 6.3-11.7 | 16 | 11.2-20.8 |
2.5 | LOW-4.17 | 9.5 | 6.65-12.35 | 16.5 | 11.55-21.45 |
3 | LOW-4.67 | 10 | 7-13 | 17 | 11.9-22.1 |
3.5 | LOW-5.17 | 10.5 | 7.35-13.65 | 17.5 | 12.25-22.75 |
4 | 2.8-5.2 | 11 | 7.7-14.3 | 18 | 12.6-23.4 |
4.5 | 3.15-5.85 | 11.5 | 8.05-14.95 | 18.5 | 12.95-24.05 |
5 | 3.5-6.5 | 12 | 8.4-15.6 | 19 | 13.3-24.7 |
5.5 | 3.85-7.15 | 12.5 | 8.75-16.25 | 19.5 | 13.65-25.35 |
6 | 4.2-7.8 | 13 | 9.1-16.9 | 20 | 14-26 |
6.5 | 4.55-8.45 | 13.5 | 9.45-17.55 | 20.5 | 14.35-26.65 |
7 | 4.9-9.1 | 14 | 9.8-18.2 | 21 | 14.7-27.3 |
7.5 | 5.25-9.75 | 14.5 | 10.15-18.85 | 21.5 | 15.05-27.95 |
8 | 5.6-10.4 | 15 | 10.5-19.5 | 22 | 15.4-28.6 |
8.5 | 5.95-11.05 | 15.5 | 10.85-20.15 | 22.2 | 15.5-HIGH |
Good fingerstick practices
When using your meter, make sure:
When using your meter, make sure:
- Your test strips are stored as directed and not expired.
- Your hands are clean for the fingerstick. Wash your hands thoroughly with soap and water (not hand gel) and dry them. Then test. There are times when the numbers temporarily don’t match but are likely to become closer over time. For example:
- Sensor’s first day. With newly inserted sensors, the differences between your meter value and the Dexcom ONE+ reading may be greater. Generally, the match gets closer over the first 24 hours.
- Glucose changing quickly. When your glucose is changing quickly, it’s more difficult to compare numbers. The meter and Dexcom ONE+ measure glucose from different sources (blood and interstitial fluid), and blood glucose changes a little before interstitial fluid glucose. The match gets closer and easier to compare when your glucose stabilizes.
- Pressure on sensor. When something is pressing on your sensor it can affect your Dexcom ONE+ readings. The match should get closer after the pressure is relieved.
Calibration
Calibrating your Dexcom ONE+ is optional. It should bring the CGM readings closer to your BG meter value. Don’t calibrate in these situations:
Calibrating your Dexcom ONE+ is optional. It should bring the CGM readings closer to your BG meter value. Don’t calibrate in these situations:
- There is pressure on the CGM: Don't calibrate if the CGM reading seems inaccurate because of pressure on the CGM. The CGM should recover on its own when the pressure is relieved.
- Unstable glucose: Calibration works best when your glucose is stable. Consider waiting to calibrate if your glucose is changing rapidly. When calibrating, make sure to:
- Clean hands: Wash your hands with soap and water and dry them.
- Enter within 5 minutes: Enter the calibration within 5 minutes of taking a fingerstick.
To calibrate your Dexcom ONE+ using your BG meter (optional):
In the app, go to Settings > Calibrate. In the receiver, go to Menu > Calibrate.
When you calibrate your Dexcom ONE+ using your BG meter, remember:
- Calibrate in one display device: Calibrate in one display device, even if you use both the app and receiver. The CGM wearable sends calibration information between them.
- Meter values: Only calibrate with BG meter values from 2.2 mmol/L to 22.2 mmol/L.
- Calibration Not Used alert: If you get a Calibration Not Used alert, take another fingerstick and calibrate again.
To determine what to do, watch your Dexcom ONE+ readings over several hours. If the readings are always higher (or always lower) than your meter values and always more than 30% difference, please submit a Product Support Request or reach out to your HCP for further assistance.
It is important to trust your own body and your symptoms. If the way you feel does not match your CGM readings, or if you have any doubts, always take a blood glucose reading for comparison.
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