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 long-term complications of diabetes. Blood sugar tests are performed with a portable electronic device that measures sugar levels 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 dangerously high or low

When to test your blood sugar

Your doctor will advise you on 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 three or more times a day if you have type 1 diabetes. Testing may be before and after certain meals, before and after exercise, before bed, and occasionally 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 one or more times a day, depending on the number of insulin doses you take. Testing is commonly done before meals, after fasting for at least eight hours and sometimes after meals if instructed by your provider. 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.

Know your target range

Your doctor will set target blood sugar test results based on several factors, including:

  • Type and severity of diabetes
  • Age
  • Duration of disease
  • Pregnancy status
  • The presence of diabetes complications
  • Overall health and the presence of other medical conditions

For many people who have diabetes, target levels are:

  • Before meals — between 70 and 130 milligrams per deciliter (mg/dL), or 4 and 7 millimoles per liter (mmol/L)
  • One to two hours after meals — lower than 180 mg/dL (10 mmol/L)
  • Fasting at least eight hours — between 90 and 130 mg/dL (5 and 7 mmol/L)
Jan. 24, 2012 See more In-depth