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How accurate is my glucose monitor?

Glucose monitoring system accuracy – what’s in a number? There are different ways to monitor your blood glucose levels – you can use a blood glucose meter, continuous glucose monitoring (CGM) or flash glucose monitoring. All of these will give you a reading of what your glucose levels are, but they take measurements in slightly different ways. Learn about the differences and how you can get the most accurate reading from your blood glucose meter.
Content last reviewed and updated: 11.12.2023

A blood glucose meter which is also known as a blood glucose monitor

Blood glucose meters vs continuous or flash glucose monitoring

Blood glucose meters, also called finger prick tests, and the sensors in continuous glucose monitors (CGM) or flash monitors take glucose readings from different parts of the blood. Because you draw a small amount of blood when you use a blood glucose meter, it measures glucose in the blood itself – known as capillary blood.

CGM or flash sensors measure the fluid between the blood vessels and cells – this is called interstitial fluid.

Capillary blood and interstitial fluid have different physiological properties. Changes in glucose levels will be seen more quickly in capillary blood than in interstitial fluid. The difference in readings between capillary blood and interstitial fluid is often called ‘lag’.

CGM and flash sensors have algorithms that account for this lag to give an accurate reading.

How accurate are CGM and flash sensors?

The accuracy of a CGM or flash sensor depends on the chemistry of the sensor, the algorithm it uses, how it’s calibrated, and the body chemistry of the person wearing it.

If your CGM or flash sensor gives you a reading that you need to act on, for example you need to treat a hypo or take a corrective dose of insulin, check the reading with a blood glucose meter before you take action.

When you check your CGM or flash reading against a reading from a blood glucose meter, the numbers won’t be exactly the same. If the numbers are pretty close, that’s great. If they are very far apart, it’s probably best to rely on the blood glucose meter result.

A blood glucose meter being used for a finger prick test

How accurate are blood glucose meters?

Blood glucose meters have to meet international standards to provide the best possible readings. Manufacturers also have to assess what substances might interfere with the results.

Like all technology, blood glucose meters aren’t perfect. There are things you can do to get the best and most accurate results from blood glucose meters.

Look after the test strips

Test strips expire so make sure you throw out any that are old or damaged. They can be affected by heat, moisture and humidity so keep them safely in their original packaging.


As well as keeping your test strips at room temperature, you should do the same for your meter.

Wash your hands

Always wash your hands with soap and water before doing a blood glucose test because food, drink or dirt on your hands can affect the result. If you’re on the go and don’t have any soap and water, try a disinfectant wipe.

Check the codes

Make sure the code on your meter matches the code on your test strip container.

Use a larger drop of blood

Not using enough blood can sometimes affect the result of your reading. Make sure you use a new test strip when you try a bigger droplet.

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