Why should I know my blood sugar levels?

A patient having a pin-prick blood test

Our Associate Medical Director Dr Mike Knapton tells Senior Cardiac Nurse Emily Reeve why it can be important to know your numbers.

Why do my blood sugar levels matter? 

We all need sugar in our blood to provide cells with energy. The hormone insulin allows sugar (glucose) in your bloodstream to enter your cells, where it can used for energy. If you don’t have enough insulin, sugar stays in the bloodstream. Over time, high blood sugar levels damage your blood vessels. This can cause other problems, such as coronary heart disease, kidney disease and diabetic eye disease. It’s important to know whether you have high blood sugar so that this can be controlled, reducing the risk of damage.

If you don’t have enough insulin, sugar stays in the bloodstream

A high blood sugar level would mean you either have diabetes (type 1 or type 2) or have a high risk of developing type 2 diabetes. Although diabetes can have symptoms, such as thirst, urinating a lot, blurred vision, weight loss, recurrent infections and tiredness, you may only get these mildly, or not at all. That’s why it’s important to get tested.

If I’ve had a heart attack, should I get my blood sugar checked?

If you have heart and circulatory disease, this should be done as part of your routine blood checks. If you are concerned, talk to your GP.

What about people who don’t have any existing conditions?

If you are at risk, your blood sugar will be tested as part of an NHS Health Check in England (for those aged 40–74 with no existing condition). Arrangements vary in the rest of the UK, but again, ask your GP if you are concerned.

Am I at risk of diabetes?

Any of the following can mean you’re at risk, especially if more than one of these applies:

  • being over the age of 40
  • south Asian, Chinese, African-Caribbean or black African background
  • a close relative has diabetes
  • overweight or large waist size
  • high blood pressure
  • pregnancy or previous gestational diabetes
  • polycystic ovary syndrome, schizophrenia, bipolar illness or depression, or you are taking antipsychotic medication.

Learn more about your diabetes risk using the Diabetes UK online tool.

What if I have diabetes?

A person testing their blood sugar with a glucose meter

Monitor your blood sugar levels at home using a glucose meter. This involves pricking your finger and applying a drop of blood to a test strip.

Self-monitoring can be a helpful part of diabetes management. Regular blood sugar tests help you see how specific changes, for example around diet and physical activity, affect blood sugar levels. Monitoring can also help your healthcare team adjust your treatment to best prevent any long-term complications. Your doctor should also check HbA1c levels at least yearly to assess long-term blood sugar control

What do my blood sugar numbers mean?

Self-monitoring can be a helpful part of diabetes management

Persistently high blood sugar usually means you have diabetes. If HbA1c is more than 48 mmol/mol or fasting blood glucose is more than 11 mmol/L, your blood sugar is high. For most people without diabetes, normal blood sugar levels are: 

  • between 4 and to 6 mmol/L before meals
  • less than 8 mmol/L two hours after eating.

If you have diabetes, it’s key for your blood sugar levels to be as near normal as possible.

How is blood sugar measured?

Your GP can test your blood for a substance called HbA1c (glycated haemoglobin), to diagnose type 2 diabetes, or to monitor long-term blood sugar control if you have diabetes. This is different from the finger-prick blood sugar test.

Measuring HbA1c gives a picture of your average blood sugar levels over the past eight to 12 weeks. If you have diabetes, your HbA1c should be tested every three, six or 12 months. The higher the HbA1c, the greater the risk of developing complications.

The test for gestational diabetes is a bit different and is called an oral glucose tolerance test. Usually you’ll be given a glucose drink and your blood sugar will be tested before and after.

Published by the BHF

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