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updated January 24, 2012

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.
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MayoClinic Logo
Filed under: Diabetes

( 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)
How to test your blood sugar

Blood sugar testing requires the use of an electronic device called a glucose meter. The meter reads the amount of sugar in a small sample of blood, usually from your finger, that you place on a disposable test strip. Your doctor or diabetes educator can recommend an appropriate device for you.

Your doctor or diabetes educator can also help you learn how to use a meter. He or she may occasionally ask you to demonstrate how you test your blood sugar to ensure you're using the device properly.

Follow the instructions that come with your glucose meter. In general, here's how the process works:

  1. Wash your hands with soap and warm water. Dry them well.
  2. Remove a test strip from the container and replace the cap to prevent damage to the strips.
  3. Insert the test strip into the meter.
  4. Prick your finger with the needle (lancet) provided with your test kit. Prick the side of your finger, rather than the tip, so that you won't have sore spots on the part of the finger you use the most.
  5. Gently squeeze or massage your finger until a drop of blood forms.
  6. Touch the test strip to the blood, but not your skin.
  7. The meter will display your blood glucose level on a screen.
Recording your results

Each time you perform a blood test, log your results in a notebook or journal. Record the date, time, test results, medication and dosage, and diet and exercise information. The American Diabetes Association provides a printable form on their web site for logging information, and there are mobile-device applications for tracking blood sugar readings.

Bring your record of results with you to all appointments with your doctor. Talk to your doctor about what to do and when to call when you get results that don't fall within the normal range of your target goals.

Avoiding problems with meter usage

Blood sugar meters need to be used and maintained properly. Follow these tips to ensure proper usage:

  • Follow the instructions in the user manual for your device, as procedures may vary from one device to another.
  • Use a blood sample size as directed in the manual because different meters require different sample sizes.
  • Change batteries as recommended by the manufacturer.
  • Use only test strips designed for your meter because not all devices and strips are compatible.
  • Store test strips as directed.
  • Don't use expired test strips.
  • Clean the device regularly as directed.
  • Run quality control tests as directed.
  • Check the manual for additional troubleshooting tips.
  • Bring the meter with you to doctor appointments to address any questions and to demonstrate how you use your meter.
©1998-2013 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.
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