Diabetes Fasting and Insulin
Your doctor has suggested you have a test that requires you to fast before the test. This means you will not eat food or drink liquids for a period of time before the test. If you have diabetes and take Insulin this Test Facts will help you fast and control your blood sugar (glucose) levels. If, after reading this information you are still unsure as to how to dose your insulin, check with the doctor who prescribes your insulin for advice.
Mealtime (Short-Acting) Insulin )Humalog®, NovoLog®, Apidra®, Humulin® R, Novolin® R)
Do not take these insulin’s on the day of the fast. Start again when you are eating meals.
Long-Acting Insulin (Lantus®, Levemir®, NPH)
If you usually take Lantus, Levemir, or NPH in the morning, take half dose on the morning of the fasting day. If you usually take Lantus, Levemir, or NPH at bedtime, take all of your usual dose the night before the fasting day. If you usually take Lantus, Levemir, or NPH at bedtime, take all of your usual dose at the usual time AFTER the fasting is over.
Insulin pump users should not take bolus insulin on the day of the fast, but should continue their basal rate. The basal rate should continue unchanged on the day of the fast. If you are worried that the basal insulin will cause low blood sugar, adjust the basal rate to 80% of the usual rate for the day of the fast.
Mixed Insulins (70/30 mix, 75/25 mix, 50/50 mix)
A general rule is to just use HALF doses on the day of the fast.
Treating Low Blood Sugar While Fasting
While fasting, check your blood sugar four times a day (at your usual mealtimes and at bedtime) or anytime you have symptoms of a low blood sugar. Common symptoms of a low blood sugar may include: shakiness, dizziness, sweating and headache. If your blood sugar drops under 70, you should immediately take 15 grams of glucose gel (1 tube). This will usually raise your blood sugar by 50 points in about 15 minutes. Be sure to re-check your blood sugar 15 minutes after treatment, to make sure it is over 70. If not, take a second tube of gel.
Treating High Blood Sugar While Fasting
If testing shows that your blood sugar is high (over 250), you may give 1 or 2 units of short-acting insulin (Humalog, NovoLog, Apidra, Humulin R, Novolin R) every 4 hours to bring it down. Re-test your blood sugar between 2 and 4 hours after giving short-acting insulin. If your blood sugar stays over 400 for more than 4 hours, call the doctor who prescribes your non-insulin medication for advice.
Driving Home After Procedures
Depending on the procedure National Jewish Health may recommend a family member or friend drive you home. If you drive home National Jewish Health strongly recommends that you check your blood sugar every time before driving a car. Your blood sugar should be 100 or higher before driving. Keep fast-acting sugar with you in your car (glucose gel, glucose tablets or hard candy).
Remember: If you are still unsure as to how to dose your insulin, check with the doctor who prescribes your insulin for advice. Bring your glucose meter and test strips to National Jewish Health on your test day.
How to Get to Your Procedure
On the day of your scheduled test, check in at the Front Desk. If you have questions before or during your test please call 303-398-1355. Also, if you need to cancel the appointment or change the time please call.
This information has been approved by Elizabeth F.O. Kern, MD, MS (September 2010).