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Diabetes: Adjusting your medicine and diet for a fasting blood test


Adjusting your diabetes medicine and diet for a fasting blood test

The goal is to prevent low blood sugar and treat it, if needed.

When you do your fasting blood test, have it as early in the morning as possible.

Day before your test

The day before your test, take your diabetes medicine (such as pills, insulin, or other medicines you inject) as usual or as your healthcare provider tells you.

Day of your test

On the morning of the test, only take your morning diabetes medicine if you take a basal insulin, such as Humulin N, Novolin NPH, Lantus, Basaglar, Toujeo, Levemir or Tresiba. Take these medicines at your regular time.

If you take any other diabetes medicine in the morning, don’t take them on the day of your test.

Test your blood sugar level before you leave home. If your blood sugar level is below 4.0 mmol/L, treat it, eat a meal, and have your blood test another day.

If your blood sugar level is what it should be, you can go to your blood test. Bring the following with you to your test:

  • a source of fast-acting sugar
  • your blood glucose meter

Test your blood sugar level at the lab. If your blood sugar level is low, please tell the person doing your blood test.

After your blood test

Test your blood sugar level before you leave the lab. Make sure it’s above 4.0 mmol/L before you drive. If it’s below 4.0 mmol/L, treat with 15 grams of carbohydrates then retest. If it’s still low, treat again.

Having a low blood sugar level can impair your driving skills, meaning they aren’t as sharp as usual. If you plan to drive after you treat a low blood sugar level:

  • Wait 40 minutes before you drive.
  • Make sure your blood sugar is 5.0 mmol/L or more before you drive.

You can take your usual morning diabetes medicine after the test is done and when you’re ready to eat.

To find out more about diabetes and driving, ask your healthcare team for the Driving and Diabetes Handout.

To see this information online and learn more, visit

For 24/7 nurse advice and general health information call Health Link at 811.

Current as of: May 1, 2018

Author: Endocrinology and Metabolism Program, Alberta Health Services

Care instructions may be adapted by your healthcare provider. If you have questions about a medical condition or this instruction, talk with your doctor or appropriate healthcare provider.