Blood sugar testing: Why, when and how

Blood sugar testing is an important part of diabetes care. Find out when to test your blood sugar level, how to use a testing meter and more.

By Mayo Clinic Staff

If you have diabetes, self-testing your blood sugar (blood glucose) can be an important tool in managing your treatment plan and preventing diabetes complications. You can test your blood sugar at home with a portable electronic device (glucose meter) that measures sugar level in a small drop of your blood.

Why test your blood sugar

Blood sugar testing — or self-monitoring blood glucose — provides useful information for diabetes management. It can help you:

  • Judge how well you're reaching overall treatment goals
  • Understand how diet and exercise affect blood sugar levels
  • Understand how other factors, such as illness or stress, affect blood sugar levels
  • Monitor the effect of diabetes medications on blood sugar levels
  • Identify blood sugar levels that are high or low

When to test your blood sugar

Your doctor will advise you how often you should check your blood sugar level. In general, the frequency of testing depends on the type of diabetes you have and your treatment plan.

  • Type 1 diabetes. Your doctor may recommend blood sugar testing four to 10 times a day if you have type 1 diabetes. You may need to test before meals and snacks, before and after exercise, before bed, and sometimes during the night. You may also need to check your blood sugar level more often if you are ill, change your daily routine or begin a new medication.
  • Type 2 diabetes. If you take insulin to manage type 2 diabetes, your doctor may recommend blood sugar testing a few times a day, depending on the type and amount of insulin you use.

    Testing is usually recommended before meals and at bedtime if you're taking multiple daily injections. You may need to test only twice daily, before breakfast and dinner if you only use a long-acting insulin. If you manage type 2 diabetes with noninsulin medications or with diet and exercise alone, you may not need to test your blood sugar daily.

What if you have a continuous glucose monitor (CGM)?

People treated with insulin, particularly those with type 1 diabetes, may also choose to use a CGM. These devices measure your blood sugar every few minutes using a sensor inserted under the skin.

Some devices show your blood sugar reading at all times on a receiver, and an alarm will go off if your blood sugar is going up or going down too quickly. Others require that you check your blood sugar by running the receiver over the sensor periodically.

Most of these devices still require finger-stick checks to calibrate the machine. Check your device's user guide to learn if you need to check, and how often you need to do so.

Jan. 26, 2018