How accurate are blood glucose meters?

Diabetes nurse educator, Christine Manga, answers the burning question: how accurate are blood glucose meters?

Blood glucose meters are an essential and convenient tool for people living with diabetes to manage their condition. These small devices allow you to measure your blood glucose levels quickly and accurately whilst on the go.

However, some people are concerned about the accuracy of these glucose meters. This is a valid concern as inaccurate readings can lead to incorrect treatment decisions, which can have serious consequences.

Trialled and tested

The accuracy of blood glucose meters has improved significantly in recent years. The accuracy of these devices is tested by regulatory bodies such as the Food and Drug Administration (FDA) in the United States before they are approved for use by the public.

Over and above this, manufacturers are also required to meet certain accuracy standards. The International Organisation for Standardisation (ISO) has established a standard for blood glucose meter accuracy which requires readings fall within 15% of a laboratory reference value. This explains why glucose readings can differ even when taken at the same time but on different fingers. Using two different meters will also yield different results due to the 15% allowance.

Blood glucose meters are generally considered to be accurate. Some meters come with a control solution that have a known glucose concentration, which you can use to test your meter’s accuracy. Newer meters don’t come with this.

Maintenance and use of the blood glucose meter

The accuracy of a blood glucose meter depends on several factors, most of which the user has control over. Included here are maintenance and use of the meter.

• Check expiry date of strips, expired strips can give inaccurate results.
• Use the meter according to the manufacturer’s instructions.
• Close the strip container securely each time as moisture/humidity can damage the strips.
• Avoid exposing strips and meters to extreme temperatures such as leaving them in a hot car or keeping them in a fridge.
• Wash and dry hands properly before testing. Contamination from food and hand creams among other things can alter glucose readings.
• Hands should be warm when testing, if they are cold, more pressure is applied to obtain the blood drop, getting some interstitial fluid (ISF) that can lead to unreliable readings.
• Dehydration can affect readings, try to drink enough fluid every day.
• Use a sufficient size blood drop, too little blood may give inaccurate results.
• Do not share your meter.

Glucose sensor vs finger-prick readings

For people who wear glucose sensors, they may notice a substantial difference between their finger prick and sensor readings. This is not due to inaccuracy of either device.

Sensor glucose and capillary blood glucose are different because they measure glucose levels using different body fluids. Sensor glucose readings come from interstitial fluid (ISF), which is the fluid that surrounds the cells under the skin.

Finger-prick blood glucose readings come from the blood that flows in the small blood vessels near the surface of the skin. There is a delay between the glucose levels in the blood and the ISF because glucose first enters the bloodstream from the digestion of food, and then diffuses into the ISF. This delay can be up to five minutes.

Therefore, sensor glucose and finger-prick blood glucose readings may not always match, especially when glucose levels are changing rapidly, such as after eating, exercising, or taking insulin. This is normal and expected.

The difference in sensor and blood glucose doesn’t matter if you understand why they may not always match and how to use them correctly. Sensor glucose readings can give you a more complete picture of your glucose trends and patterns over time as they test your glucose every 60 seconds, while capillary blood glucose readings can give you a more precise measurement of your glucose level at a specific moment.

Ask for advice

If you are concerned about the accuracy of your readings, you should talk to your doctor or diabetes educator for advice. They can help you choose a meter and test strips and teach you how to use them correctly.

As another option, you can do a finger-prick test on your meter at the same time as you have blood drawn in a lab and compare the results. They should be within 15% of each other.

Blood glucose meters are fantastic devices that assist in day-to-day management of diabetes. They have without a doubt evolved over time.

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