How accurate is your blood glucose meter?
Wednesday, 17 May 2017
How does your glucose meter work?
We’ve come a long way from the days when urine strips only displayed a result when your glucose levels were high enough to spill over into your urine. But how accurate are today’s blood glucose meters?
When you place your blood on a strip, the glucose in that sample reacts with the chemicals in the strip setting up a small electrical current, which the meter reads. The more glucose that is in the sample the higher the current and the higher the reading.
When you consider the delicate components in the strip, such as the size of the strip and blood sample and the size of the meter, it is a wonder of technology that readings can be as accurate as they are.
In placing and keeping a blood glucose meter on the market, meter makers must obey the International Organization for Standardization (ISO).
These standards are enforced by Australia’s own governing body the Therapeutic Goods Administration (TGA), which from time to time will recall these products when they don’t meet certain conditions.
In 2013, new regulations for meter accuracy were agreed. These standards were enforced in 2016. Project leader, Dr Alan Cariski, comments, “More accurate glucose measurements will help patients to better regulate their diabetes through more informed treatment decisions that may affect, for example, dietary intake and medication dose, especially insulin.” (Lazarte, 2013)
What does this mean for you?
In meters, readings greater than 4.2 mmol/l, must have an accuracy of +-15 per cent for 99 per cent of readings.
However, let’s translate this to real life with a couple of examples:
- Your blood glucose meter reading of 10.0mmol/l really may range from 11.5 to 8.5mmol/l for 99 per cent of readings
- Your blood glucose meter reading of 4.2mmol/l really may range from 4.8 to 3.6 mmol/l for 99 per cent of readings.
This also suggests that in the same blood drop if you used two different meters, readings may differ by up to 30 per cent. Many blood glucose meters have much better accuracy than this minimum standard, and therefore are accurate enough for you to base your decisions.
Some facts to consider
Results of blood glucose will differ from each finger, body site and from minute to minute. Blood flows constantly through our skin and turnover is fast. Blood gets to different sites in your body at different times and as blood travels glucose leaves. This may be important if you are not always using the sides of your fingers to check blood glucose. Blood glucose can rise and fall quickly according to meal, insulin, exercise, etc.
- Readings differ with the level of red blood cells in your blood (haematocrit). Some medications may change results as well.
- Maintenance of your meter is important. Clean and calibrate (with control solution) as per your manufacturer’s recommendation.
- Check the expiry date of your strips. Ensure strips have been kept at the conditions suggested by your manufacturer on the packaging. Temperature, humidity and altitude will alter your readings.
- As results will differ from meter to meter, base your blood glucose decision on one meter. You may require another meter to check ketones and keep a back-up meter.
- You cannot compare results from continuous glucose monitoring or flash monitoring with blood glucose readings. The first two monitoring systems read the glucose between cells in the skin layer, which rises and falls slower than your blood glucose by 5-7 minutes.
- Check your monitoring technique. If you have food, moisturiser or hand sanitiser on your hands it will affect your readings.
- If you are unsure if a meter is working correctly, call the manufacturer or you can contact Diabetes Queensland on 1800 177 055