Blood Glucose Testing


Blood Glucose Testing

Many people think they can tell what their blood glucose (sometimes called blood sugar) levels are by how they feel. But, some people can feel "high" when their blood glucose levels are low, and some can feel "low" when their blood glucose levels are normal or high. The only way to know for sure is to test your blood glucose levels.

The body makes glucose from the sugary and starchy foods that you eat, but diabetes changes the way your body controls your blood glucose. Blood glucose levels are also affected by other things, such as activity, changes in medication (tablets / insulin), illness and stress.

Research shows that keeping blood glucose levels within an acceptable target range helps prevent the complications associated with diabetes. You can lower your risk of eye problems, kidney disease, nerve damage, and heart problems. Understanding how to balance your blood glucose levels may also help you feel better day to day.

What is blood glucose testing?

A blood glucose test is carried out using a blood glucose meter, sometimes called a blood glucose monitor. A blood glucose test tells you how much glucose is in your blood at any given time. A blood glucose test is performed simply and easily by pricking the side of your finger with a lancet to form a drop of blood. A test strip is inserted into the blood glucose meter and the strip sips in the blood for the meter to test. The blood glucose meter will then count down and display the result.

Why do a blood glucose test?

You will need to measure your blood glucose levels to help you and your diabetes team decide how best to manage your diabetes and to assess how well your treatment is working. You will be advised of ways to keep your blood glucose levels as close to normal as possible by managing your food intake, exercising and / or by taking medication.

Blood glucose monitoring provides you with a picture of your blood glucose control and indicates when changes occur. By self-testing regularly, recording your results and reviewing them with your diabetes care team, you will learn to adjust your diabetes management to maintain your blood glucose levels within agreed targets.

When to test

You should discuss the timing and frequency of blood glucose monitoring with your diabetes care team. You need to carry out enough tests to show your overall blood glucose trends so that you and your diabetes care team can see how well your treatment and management are working and where adjustments might be helpful. The times you need to test should be agreed between you and your care team (e.g. before / after meals), and you should keep a note of the results in your glucose testing record diary. You can also use Ascensia's GLUCOFACTS® Deluxe software to help you understand your results.

At times you may need to increase the number of blood glucose tests you take to get more information and give you a better picture of what is going on, e.g. when you are unwell, following medication changes, at times of increased activity or at times of stress. Be prepared to perform a blood glucose test before you drive to make sure that your blood glucose levels have not change unexpectedly, which would make it unsafe to be in control of a vehicle.

Target levels

You should agree your target blood glucose levels with your diabetes care team. Discuss realistic targets for various times of the day and activities to ensure that you are safe at all times.

Top blood glucose testing tips

  • Always follow the manufacturer’s instructions for your blood glucose meter
  • Check the expiry date on all diabetes testing supplies
  • Wash your hands thoroughly with warm soapy water and dry carefully before glucose testing. This will help get rid of any contaminants (e.g. sugar on your fingers from the food you have been eating), and will also ensure a good blood flow
  • Use the sides of your fingers, as these are less sensitive than the fingertips. Avoid the thumb and index finger and vary the sites to avoid the risk of infection or callous build up
  • If you struggle to obtain enough blood, hold your hand down to let gravity help the blood flow to the fingers
  • Change the lancet in the finger-pricking device every time you perform a blood glucose test. This will reduce discomfort, the risk of infection and ensure that enough blood is obtained
  • Record the results in your glucose testing record diary
  • Make a note of anything unusual alongside the results and whether they were taken before or after meals. Later on, it is not always easy to remember what else might have been happening at the time of the blood glucose test
  • Take your glucose testing record diary, or print out from your GLUCOFACTS® Deluxe diabetes management software (a tracking tool that helps you monitor your blood glucose levels), to all appointments with your diabetes care team.

Understanding your results

In order to use your blood glucose results to guide management successfully, you need to understand how to interpret them. Here are some points to help you do this:

  • Glucose monitoring systems: different glucose monitoring devices or blood glucose meters use different methods to measure blood glucose levels and may give different results, even if the blood glucose tests have been performed correctly and at the same time. Use only one type of glucose monitoring device to obtain an overall picture of your blood glucose trends
  • Laboratory results versus self-monitoring: blood samples sent to the hospital laboratory for analysis may return results that are 10-15% higher than the results you get from a blood glucose meter. This is because some older blood glucose meters report whole blood glucose referenced results whereas laboratory systems report plasma referenced results.
  • Test and check the results: some people think they can tell what their blood glucose levels are by how they feel, but this is often not the case and you should always test to be sure. If your blood glucose test result does not match the way your feel, retest your blood glucose levels and make sure the test is performed as instructed by the manufacturer of the glucose monitoring device
  • Timing of blood glucose monitoring: it takes about 2 hours before you can tell the effect that your meal has had on your blood glucose levels. Blood glucose tests carried out immediately after eating will not really provide any useful information.
    • If your blood glucose levels are higher than your agreed target range 2 hours after eating, your carbohydrate servings may have been too large, or your medication dose could have been inadequate for that meal. You should discuss this with your diabetes care team.
    • Blood glucose levels can be lower than normal after exercise, and may remain lower than normal for several hours. If your blood glucose increases after exercise, you may need to adjust your medication (discuss this with your diabetes care team)
    • Your results can be affected by illness, hormonal changes (e.g. during the night, menopause, menstrual cycles), stress, changes in medication, changes in dietary intake and reduced levels of physical activity. Discuss changes in your blood glucose levels with your diabetes care team.

What is HbA1c?

HbA1c (glycosylated haemoglobin) is a measure of the amount of glucose attached to the body’s red blood cells; it is present in everyone. It gives an indication of your blood glucose control over the last 3 months. The level of HbA1c in your body rises and falls in line with your blood glucose – the higher your HbA1c, the more glucose is attached to your red blood cells. Your HbA1c does not change rapidly because the red blood cells in your circulation last for around 3–4 months. Any increases and decreases in your HbA1c will happen over a period of at least 6 weeks.

Your HbA1c results is recorded in mmol/mol. It was recorded as a percentage (%) until 2011.

HbA1c monitoring

Your diabetes team will check your HbA1c regularly during clinic visits. You should talk to your team about the target HbA1c you want to achieve given your lifestyle, activity level and age.

HbA1c and blood glucose

The chart below shows the relationship between the blood glucose level that you measure yourself and your HbA1c measurements from the hospital.

HbA1c level (%)

HbA1c level (mmol/mol)

Average plasma glucose level


42 mmol/mol

7.5 mmol/L


53 mmol/mol

9.4 mmol/L


64 mmol/mol

11.3 mmol/L


75 mmol/mol

13.3 mmol/L


86 mmol/mol

15.3 mmol/L


97 mmol/mol

17.2 mmol/L


108 mmol/mol

19.1 mmol/L

Research shows that improved control of HbA1c will decrease the risk of diabetes complications.*

Find out what your HbA1c is and keep a record of it in your glucose testing record diary. Remember, the better your blood glucose control, the more likely you are to achieve your HbA1c target.

Top tips

Remember that:

  • Blood glucose monitoring alone does not improve your diabetes. It is how you use the information from your glucose testing that makes the difference to your diabetes control
  • Changes in your HbA1c will happen over a period of at least 6 weeks; do not expect to see immediate changes in response to changes you make to your diabetes management
  • Improving your HbA1c control can help decrease your risk of developing complications associated with your diabetes
  • Make sure you discuss with your diabetes care team how often you need to have your HbA1c tested to help you gain control of your blood glucose.
  • References: Ferenczi, Reddy, Lorber (2001) Effect of Immediate Hemoglobin A1c Results on Treatment Decisions in Office Practice. Endocrine Practice, 7(2).Stratton IM et al. UKPDS 35. BMJ 2000;321:405-412


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