User guide

troubleshooting basics
troubleshooting basics
2726
Sensor vs. Meter BG
Discrepancy between sensor and meter BG. Possible causes:
• A new sensor has to settle into the tissue, and requires 2 calibrations within the rst 6 hours
• Sensor placed late in the day/evening and not calibrated till morning
• Meter variance – make sure you don’t use dierent meters
• Rapidly rising blood glucose. ‘Sensor Lag’ between uid compartments
• Unrealistic expectations
• Sensor value is an average over 5 minutes. Meter value is a single point in time
There will always be a dierence between interstitial glucose and blood glucose. Let’s explain what
is actually happening when a value is provided. The sensor reads the interstitial glucose in electrical
values. The meter reads the blood glucose in mmol/L. When a calibration is entered, the electrical
signal (also known as a Signal Current or ISIG) at that time is paired to that blood glucose entry. Then
as the ISIG rises or falls, the sensor provides a value based on its relative scale.
For example:
If you enter a meter BG of 5.2 mmol/L and the current ISIG is 100 nA, a calculation
is made to pair these values. If, a few minutes later, the ISIG has risen to 119 nA
the sensor will show a reading of something like 5.7 mmol/L or conversely, the
ISIG drops to 75 nA, the value read o the pump will be more in the range of
4.6 mmol/L as an example.
Making Sense of BG vs.
Sensor Discrepancy
With early sensor use there is a gradual increase in understanding of the system. Your healthcare
provider and the Medtronic 24-hour Product Helpline are there to support you during the early days
and beyond.
As you become more familiar and comfortable with the system, you will experience greater
condence. This is due to the realisation that:
• The trends indicated by the arrows are more important than the ‘point to point’
comparison
• The alert thresholds can help you identify behaviours which lead to alarms – change
your behaviours, control your excursions and get closer meter to sensor values
Calibration Error
What is a CAL ERROR Alarm?
A CAL ERROR alarm may occur 10 to 15 minutes after a meter BG is entered into the insulin pump.
It means there is a signicant dierence between your meter BG and the sensor glucose reading.
This will sometimes happen if your glucose is changing quickly. It may also happen if there is a
problem with the glucose sensor.
What should you do if you get a CAL ERROR Alarm?
• Wait at least 15 minutes to make sure that your BG is not changing rapidly. Are there
any arrows on the screen? Then do another ngerstick BG for calibration. You may
need to wait even longer before you do this second ngerstick
• If you do need to test your BG before the 15 minutes has passed to take care of your
diabetes (e.g. to check for a low BG), then perform the test. However, it is best that
you not use the results of the test for calibration
• If you get two CAL ERROR alarms in a row, you will get a CHANGE SENSOR or SENSOR
END message telling you to replace the glucose sensor, which may be unnecessary.
This is why you want to wait until your BG has become more stable before entering
the next ngerstick BG calibration
Common pitfalls in terms of calibration
• Entering the same calibration value twice in a row within a few minutes
• Using more than one meter to enter calibrations
• Entering too many calibrations over a 24 hour period
• ‘Rounding o’ calibration values
• Inserting the sensor in too late in the day to enter the recommended two calibrations
in the rst 6 hours
• Entering a calibration during a period of rapid glucose change as indicated by two
trend arrows up or down